Release: 1.4.44 | Release Date: November 12, 2022

# SQLAlchemy 1.4 Documentation

# 0.9 Changelog

## 0.9.10

Released: July 22, 2015

### orm

- [orm] [feature]

  Added a new entry `"entity"` to the dictionaries returned by `Query.column_descriptions`. This refers to the primary ORM mapped class or aliased class that is referred to by the expression. Compared to the existing entry for `"type"`, it will always be a mapped entity, even if extracted from a column expression, or None if the given expression is a pure core expression. See also #3403 which repaired a regression in this feature which was unreleased in 0.9.10 but was released in the 1.0 version.

  References: #3320

- [orm] [bug]

  `Query` doesn’t support joins, subselects, or special FROM clauses when using the `Query.update()` or `Query.delete()` methods; instead of silently ignoring these fields if methods like `Query.join()` or `Query.select_from()` has been called, a warning is emitted. As of 1.0.0b5 this will raise an error.

  References: #3349

- [orm] [bug]

  Fixed bug where the state tracking within multiple, nested `Session.begin_nested()` operations would fail to propagate the “dirty” flag for an object that had been updated within the inner savepoint, such that if the enclosing savepoint were rolled back, the object would not be part of the state that was expired and therefore reverted to its database state.

  References: #3352

### engine

- [engine] [bug]

  Added the string value `"none"` to those accepted by the `Pool.reset_on_return` parameter as a synonym for `None`, so that string values can be used for all settings, allowing utilities like `engine_from_config()` to be usable without issue.

  References: #3375

### sql

- [sql] [feature]

  Added official support for a CTE used by the SELECT present inside of `Insert.from_select()`. This behavior worked accidentally up until 0.9.9, when it no longer worked due to unrelated changes as part of #3248. Note that this is the rendering of the WITH clause after the INSERT, before the SELECT; the full functionality of CTEs rendered at the top level of INSERT, UPDATE, DELETE is a new feature targeted for a later release.

  References: #3418

- [sql] [bug]

  Fixed issue where a `MetaData` object that used a naming convention would not properly work with pickle. The attribute was skipped leading to inconsistencies and failures if the unpickled `MetaData` object were used to base additional tables from.

  References: #3362

### postgresql

- [postgresql] [bug]

  Fixed a long-standing bug where the `Enum` type as used with the psycopg2 dialect in conjunction with non-ascii values and `native_enum=False` would fail to decode return results properly. This stemmed from when the PG `ENUM` type used to be a standalone type without a “non native” option.

  References: #3354

### mysql

- [mysql] [bug] [pymysql]

  Fixed unicode support for PyMySQL when using an “executemany” operation with unicode parameters. SQLAlchemy now passes both the statement as well as the bound parameters as unicode objects, as PyMySQL generally uses string interpolation internally to produce the final statement, and in the case of executemany does the “encode” step only on the final statement.

  References: #3337

- [mysql] [bug] [py3k]

  Fixed the `BIT` type on Py3K which was not using the `ord()` function correctly. Pull request courtesy David Marin.

  References: #3333

### sqlite

- [sqlite] [bug]

  Fixed bug in SQLite dialect where reflection of UNIQUE constraints that included non-alphabetic characters in the names, like dots or spaces, would not be reflected with their name.

  References: #3495

### tests

- [tests] [bug] [pypy]

  Fixed an import that prevented “pypy setup.py test” from working correctly.

  References: #3406

### misc

- [bug] [ext]

  Fixed bug where when using extended attribute instrumentation system, the correct exception would not be raised when `class_mapper()` were called with an invalid input that also happened to not be weak referencable, such as an integer.

  References: #3408

- [bug] [ext]

  Fixed regression from 0.9.9 where the `as_declarative()` symbol was removed from the `sqlalchemy.ext.declarative` namespace.

  References: #3324

## 0.9.9

Released: March 10, 2015

### orm

- [orm] [feature]

  Added new parameter `Session.connection.execution_options` which may be used to set up execution options on a `Connection` when it is first checked out, before the transaction has begun. This is used to set up options such as isolation level on the connection before the transaction starts.

  See also

  Setting Transaction Isolation Levels / DBAPI AUTOCOMMIT - new documentation section detailing best practices for setting transaction isolation with sessions.

  References: #3296

- [orm] [feature]

  Added new method `Session.invalidate()`, functions similarly to `Session.close()`, except also calls `Connection.invalidate()` on all connections, guaranteeing that they will not be returned to the connection pool. This is useful in situations e.g. dealing with gevent timeouts when it is not safe to use the connection further, even for rollbacks.

- [orm] [bug]

  Fixed bugs in ORM object comparisons where comparison of many-to-one `!= None` would fail if the source were an aliased class, or if the query needed to apply special aliasing to the expression due to aliased joins or polymorphic querying; also fixed bug in the case where comparing a many-to-one to an object state would fail if the query needed to apply special aliasing due to aliased joins or polymorphic querying.

  References: #3310

- [orm] [bug]

  Fixed bug where internal assertion would fail in the case where an `after_rollback()` handler for a `Session` incorrectly adds state to that `Session` within the handler, and the task to warn and remove this state (established by #2389) attempts to proceed.

  References: #3309

- [orm] [bug]

  Fixed bug where TypeError raised when `Query.join()` called with unknown kw arguments would raise its own TypeError due to broken formatting. Pull request courtesy Malthe Borch.

- [orm] [bug]

  Fixed bug in lazy loading SQL construction whereby a complex primaryjoin that referred to the same “local” column multiple times in the “column that points to itself” style of self-referential join would not be substituted in all cases. The logic to determine substitutions here has been reworked to be more open-ended.

  References: #3300

- [orm] [bug]

  The “wildcard” loader options, in particular the one set up by the `load_only()` option to cover all attributes not explicitly mentioned, now takes into account the superclasses of a given entity, if that entity is mapped with inheritance mapping, so that attribute names within the superclasses are also omitted from the load. Additionally, the polymorphic discriminator column is unconditionally included in the list, just in the same way that primary key columns are, so that even with load_only() set up, polymorphic loading of subtypes continues to function correctly.

  References: #3287

- [orm] [bug] [pypy]

  Fixed bug where if an exception were thrown at the start of a `Query` before it fetched results, particularly when row processors can’t be formed, the cursor would stay open with results pending and not actually be closed. This is typically only an issue on an interpreter like PyPy where the cursor isn’t immediately GC’ed, and can in some circumstances lead to transactions/ locks being open longer than is desirable.

  References: #3285

- [orm] [bug]

  Fixed a leak which would occur in the unsupported and highly non-recommended use case of replacing a relationship on a fixed mapped class many times, referring to an arbitrarily growing number of target mappers. A warning is emitted when the old relationship is replaced, however if the mapping were already used for querying, the old relationship would still be referenced within some registries.

  References: #3251

- [orm] [bug] [sqlite]

  Fixed bug regarding expression mutations which could express itself as a “Could not locate column” error when using `Query` to select from multiple, anonymous column entities when querying against SQLite, as a side effect of the “join rewriting” feature used by the SQLite dialect.

  References: #3241

- [orm] [bug]

  Fixed bug where the ON clause for `Query.join()`, and `Query.outerjoin()` to a single-inheritance subclass using `of_type()` would not render the “single table criteria” in the ON clause if the `from_joinpoint=True` flag were set.

  References: #3232

### examples

- [examples] [bug]

  Updated the Versioning with a History Table example such that mapped columns are re-mapped to match column names as well as grouping of columns; in particular, this allows columns that are explicitly grouped in a same-column-named joined inheritance scenario to be mapped in the same way in the history mappings, avoiding warnings added in the 0.9 series regarding this pattern and allowing the same view of attribute keys.

- [examples] [bug]

  Fixed a bug in the examples/generic_associations/discriminator_on_association.py example, where the subclasses of AddressAssociation were not being mapped as “single table inheritance”, leading to problems when trying to use the mappings further.

### engine

- [engine] [feature]

  Added new user-space accessors for viewing transaction isolation levels; `Connection.get_isolation_level()`, `Connection.default_isolation_level`.

- [engine] [bug]

  Fixed bug in `Connection` and pool where the `Connection.invalidate()` method, or an invalidation due to a database disconnect, would fail if the `isolation_level` parameter had been used with `Connection.execution_options()`; the “finalizer” that resets the isolation level would be called on the no longer opened connection.

  References: #3302

- [engine] [bug]

  A warning is emitted if the `isolation_level` parameter is used with `Connection.execution_options()` when a `Transaction` is in play; DBAPIs and/or SQLAlchemy dialects such as psycopg2, MySQLdb may implicitly rollback or commit the transaction, or not change the setting til next transaction, so this is never safe.

  References: #3296

### sql

- [sql] [bug]

  Added the `native_enum` flag to the `__repr__()` output of `Enum`, which is mostly important when using it with Alembic autogenerate. Pull request courtesy Dimitris Theodorou.

- [sql] [bug]

  Fixed bug where using a `TypeDecorator` that implemented a type that was also a `TypeDecorator` would fail with Python’s “Cannot create a consistent method resolution order (MRO)” error, when any kind of SQL comparison expression were used against an object using this type.

  References: #3278

- [sql] [bug]

  Fixed issue where the columns from a SELECT embedded in an INSERT, either through the values clause or as a “from select”, would pollute the column types used in the result set produced by the RETURNING clause when columns from both statements shared the same name, leading to potential errors or mis-adaptation when retrieving the returning rows.

  References: #3248

### schema

- [schema] [bug]

  Fixed bug in 0.9’s foreign key setup system, such that the logic used to link a `ForeignKey` to its parent could fail when the foreign key used “link_to_name=True” in conjunction with a target `Table` that would not receive its parent column until later, such as within a reflection + “useexisting” scenario, if the target column in fact had a key value different from its name, as would occur in reflection if column reflect events were used to alter the .key of reflected `Column` objects so that the link_to_name becomes significant. Also repaired support for column type via FK transmission in a similar way when target columns had a different key and were referenced using link_to_name.

  References: #1765, #3298

### postgresql

- [postgresql] [feature]

  Added support for the `CONCURRENTLY` keyword with PostgreSQL indexes, established using `postgresql_concurrently`. Pull request courtesy Iuri de Silvio.

  See also

  Indexes with CONCURRENTLY

- [postgresql] [bug]

  Repaired support for PostgreSQL UUID types in conjunction with the ARRAY type when using psycopg2. The psycopg2 dialect now employs use of the psycopg2.extras.register_uuid() hook so that UUID values are always passed to/from the DBAPI as UUID() objects. The `UUID.as_uuid` flag is still honored, except with psycopg2 we need to convert returned UUID objects back into strings when this is disabled.

  References: #2940

- [postgresql] [bug]

  Added support for the `postgresql.JSONB` datatype when using psycopg2 2.5.4 or greater, which features native conversion of JSONB data so that SQLAlchemy’s converters must be disabled; additionally, the newly added psycopg2 extension `extras.register_default_jsonb` is used to establish a JSON deserializer passed to the dialect via the `json_deserializer` argument. Also repaired the PostgreSQL integration tests which weren’t actually round-tripping the JSONB type as opposed to the JSON type. Pull request courtesy Mateusz Susik.

- [postgresql] [bug]

  Repaired the use of the “array_oid” flag when registering the HSTORE type with older psycopg2 versions < 2.4.3, which does not support this flag, as well as use of the native json serializer hook “register_default_json” with user-defined `json_deserializer` on psycopg2 versions < 2.5, which does not include native json.

- [postgresql] [bug]

  Fixed bug where PostgreSQL dialect would fail to render an expression in an `Index` that did not correspond directly to a table-bound column; typically when a `text()` construct was one of the expressions within the index; or could misinterpret the list of expressions if one or more of them were such an expression.

  References: #3174

### mysql

- [mysql] [change]

  The `gaerdbms` dialect is no longer necessary, and emits a deprecation warning. Google now recommends using the MySQLdb dialect directly.

  References: #3275

- [mysql] [bug]

  Added a version check to the MySQLdb dialect surrounding the check for ‘utf8_bin’ collation, as this fails on MySQL server < 5.0.

  References: #3274

### sqlite

- [sqlite] [feature]

  Added support for partial indexes (e.g. with a WHERE clause) on SQLite. Pull request courtesy Kai Groner.

  See also

  Partial Indexes

- [sqlite] [feature]

  Added a new SQLite backend for the SQLCipher backend. This backend provides for encrypted SQLite databases using the pysqlcipher Python driver, which is very similar to the pysqlite driver.

  See also

  `pysqlcipher`

### misc

- [bug] [ext] [py3k]

  Fixed bug where the association proxy list class would not interpret slices correctly under Py3K. Pull request courtesy Gilles Dartiguelongue.

## 0.9.8

Released: October 13, 2014

### orm

- [orm] [bug] [engine]

  Fixed bug that affected generally the same classes of event as that of #3199, when the `named=True` parameter would be used. Some events would fail to register, and others would not invoke the event arguments correctly, generally in the case of when an event was “wrapped” for adaption in some other way. The “named” mechanics have been rearranged to not interfere with the argument signature expected by internal wrapper functions.

  References: #3197

- [orm] [bug]

  Fixed bug that affected many classes of event, particularly ORM events but also engine events, where the usual logic of “de duplicating” a redundant call to `listen()` with the same arguments would fail, for those events where the listener function is wrapped. An assertion would be hit within registry.py. This assertion has now been integrated into the deduplication check, with the added bonus of a simpler means of checking deduplication across the board.

  References: #3199

- [orm] [bug]

  Fixed warning that would emit when a complex self-referential primaryjoin contained functions, while at the same time remote_side was specified; the warning would suggest setting “remote side”. It now only emits if remote_side isn’t present.

  References: #3194

### orm declarative

- [orm] [declarative] [bug]

  Fixed “‘NoneType’ object has no attribute ‘concrete’” error when using `AbstractConcreteBase` in conjunction with a subclass that declares `__abstract__`.

  References: #3185

### engine

- [engine] [bug]

  The execution options passed to an `Engine` either via `create_engine.execution_options` or `Engine.update_execution_options()` are not passed to the special `Connection` used to initialize the dialect within the “first connect” event; dialects will usually perform their own queries in this phase, and none of the current available options should be applied here. In particular, the “autocommit” option was causing an attempt to autocommit within this initial connect which would fail with an AttributeError due to the non-standard state of the `Connection`.

  References: #3200

- [engine] [bug]

  The string keys that are used to determine the columns impacted for an INSERT or UPDATE are now sorted when they contribute towards the “compiled cache” cache key. These keys were previously not deterministically ordered, meaning the same statement could be cached multiple times on equivalent keys, costing both in terms of memory as well as performance.

  References: #3165

### sql

- [sql] [bug]

  Fixed bug where a fair number of SQL elements within the sql package would fail to `__repr__()` successfully, due to a missing `description` attribute that would then invoke a recursion overflow when an internal AttributeError would then re-invoke `__repr__()`.

  References: #3195

- [sql] [bug]

  An adjustment to table/index reflection such that if an index reports a column that isn’t found to be present in the table, a warning is emitted and the column is skipped. This can occur for some special system column situations as has been observed with Oracle.

  References: #3180

- [sql] [bug]

  Fixed bug in CTE where `literal_binds` compiler argument would not be always be correctly propagated when one CTE referred to another aliased CTE in a statement.

  References: #3154

- [sql] [bug]

  Fixed 0.9.7 regression caused by #3067 in conjunction with a mis-named unit test such that so-called “schema” types like `Boolean` and `Enum` could no longer be pickled.

  References: #3067, #3144

### postgresql

- [postgresql] [feature] [pg8000]

  Support is added for “sane multi row count” with the pg8000 driver, which applies mostly to when using versioning with the ORM. The feature is version-detected based on pg8000 1.9.14 or greater in use. Pull request courtesy Tony Locke.

- [postgresql] [bug]

  A revisit to this issue first patched in 0.9.5, apparently psycopg2’s `.closed` accessor is not as reliable as we assumed, so we have added an explicit check for the exception messages “SSL SYSCALL error: Bad file descriptor” and “SSL SYSCALL error: EOF detected” when detecting an is-disconnect scenario. We will continue to consult psycopg2’s connection.closed as a first check.

  References: #3021

- [postgresql] [bug]

  Fixed bug where PostgreSQL JSON type was not able to persist or otherwise render a SQL NULL column value, rather than a JSON-encoded `'null'`. To support this case, changes are as follows:

  - The value `null()` can now be specified, which will always result in a NULL value resulting in the statement.

  - A new parameter `JSON.none_as_null` is added, which when True indicates that the Python `None` value should be persisted as SQL NULL, rather than JSON-encoded `'null'`.

  Retrieval of NULL as None is also repaired for DBAPIs other than psycopg2, namely pg8000.

  References: #3159

- [postgresql] [bug]

  The exception wrapping system for DBAPI errors can now accommodate non-standard DBAPI exceptions, such as the psycopg2 TransactionRollbackError. These exceptions will now be raised using the closest available subclass in `sqlalchemy.exc`, in the case of TransactionRollbackError, `sqlalchemy.exc.OperationalError`.

  References: #3075

- [postgresql] [bug]

  Fixed bug in `array` object where comparison to a plain Python list would fail to use the correct array constructor. Pull request courtesy Andrew.

  References: #3141

- [postgresql] [bug]

  Added a supported `FunctionElement.alias()` method to functions, e.g. the `func` construct. Previously, behavior for this method was undefined. The current behavior mimics that of pre-0.9.4, which is that the function is turned into a single-column FROM clause with the given alias name, where the column itself is anonymously named.

  References: #3137

### mysql

- [mysql] [bug] [mysqlconnector]

  Mysqlconnector as of version 2.0, probably as a side effect of the python 3 merge, now does not expect percent signs (e.g. as used as the modulus operator and others) to be doubled, even when using the “pyformat” bound parameter format (this change is not documented by Mysqlconnector). The dialect now checks for py2k and for mysqlconnector less than version 2.0 when detecting if the modulus operator should be rendered as `%%` or `%`.

- [mysql] [bug] [mysqlconnector]

  Unicode SQL is now passed for MySQLconnector version 2.0 and above; for Py2k and MySQL < 2.0, strings are encoded.

### sqlite

- [sqlite] [bug]

  When selecting from a UNION using an attached database file, the pysqlite driver reports column names in cursor.description as ‘dbname.tablename.colname’, instead of ‘tablename.colname’ as it normally does for a UNION (note that it’s supposed to just be ‘colname’ for both, but we work around it). The column translation logic here has been adjusted to retrieve the rightmost token, rather than the second token, so it works in both cases. Workaround courtesy Tony Roberts.

  References: #3211

### mssql

- [mssql] [bug]

  Fixed the version string detection in the pymssql dialect to work with Microsoft SQL Azure, which changes the word “SQL Server” to “SQL Azure”.

  References: #3151

### oracle

- [oracle] [bug]

  Fixed long-standing bug in Oracle dialect where bound parameter names that started with numbers would not be quoted, as Oracle doesn’t like numerics in bound parameter names.

  References: #2138

### misc

- [bug] [declarative]

  Fixed an unlikely race condition observed in some exotic end-user setups, where the attempt to check for “duplicate class name” in declarative would hit upon a not-totally-cleaned-up weak reference related to some other class being removed; the check here now ensures the weakref still references an object before calling upon it further.

  References: #3208

- [bug] [ext]

  Fixed bug in ordering list where the order of items would be thrown off during a collection replace event, if the reorder_on_append flag were set to True. The fix ensures that the ordering list only impacts the list that is explicitly associated with the object.

  References: #3191

- [bug] [ext]

  Fixed bug where `MutableDict` failed to implement the `update()` dictionary method, thus not catching changes. Pull request courtesy Matt Chisholm.

- [bug] [ext]

  Fixed bug where a custom subclass of `MutableDict` would not show up in a “coerce” operation, and would instead return a plain `MutableDict`. Pull request courtesy Matt Chisholm.

- [bug] [pool]

  Fixed bug in connection pool logging where the “connection checked out” debug logging message would not emit if the logging were set up using `logging.setLevel()`, rather than using the `echo_pool` flag. Tests to assert this logging have been added. This is a regression that was introduced in 0.9.0.

  References: #3168

## 0.9.7

Released: July 22, 2014

### orm

- [orm] [bug] [eagerloading]

  Fixed a regression caused by #2976 released in 0.9.4 where the “outer join” propagation along a chain of joined eager loads would incorrectly convert an “inner join” along a sibling join path into an outer join as well, when only descendant paths should be receiving the “outer join” propagation; additionally, fixed related issue where “nested” join propagation would take place inappropriately between two sibling join paths.

  References: #3131

- [orm] [bug]

  Fixed a regression from 0.9.0 due to #2736 where the `Query.select_from()` method no longer set up the “from entity” of the `Query` object correctly, so that subsequent `Query.filter_by()` or `Query.join()` calls would fail to check the appropriate “from” entity when searching for attributes by string name.

  References: #2736, #3083

- [orm] [bug]

  The “evaluator” for query.update()/delete() won’t work with multi-table updates, and needs to be set to synchronize_session=False or synchronize_session=’fetch’; a warning is now emitted. In 1.0 this will be promoted to a full exception.

  References: #3117

- [orm] [bug]

  Fixed bug where items that were persisted, deleted, or had a primary key change within a savepoint block would not participate in being restored to their former state (not in session, in session, previous PK) after the outer transaction were rolled back.

  References: #3108

- [orm] [bug]

  Fixed bug in subquery eager loading in conjunction with `with_polymorphic()`, the targeting of entities and columns in the subquery load has been made more accurate with respect to this type of entity and others.

  References: #3106

- [orm] [bug]

  Fixed bug involving dynamic attributes, that was again a regression of #3060 from version 0.9.5. A self-referential relationship with lazy=’dynamic’ would raise a TypeError within a flush operation.

  References: #3099

### engine

- [engine] [feature]

  Added new event `ConnectionEvents.handle_error()`, a more fully featured and comprehensive replacement for `ConnectionEvents.dbapi_error()`.

  References: #3076

### sql

- [sql] [bug]

  Fixed bug in `Enum` and other `SchemaType` subclasses where direct association of the type with a `MetaData` would lead to a hang when events (like create events) were emitted on the `MetaData`.

  This change is also backported to: 0.8.7

  References: #3124

- [sql] [bug]

  Fixed a bug within the custom operator plus `TypeEngine.with_variant()` system, whereby using a `TypeDecorator` in conjunction with variant would fail with an MRO error when a comparison operator was used.

  This change is also backported to: 0.8.7

  References: #3102

- [sql] [bug]

  Fix bug in naming convention feature where using a check constraint convention that includes `constraint_name` would then force all `Boolean` and `Enum` types to require names as well, as these implicitly create a constraint, even if the ultimate target backend were one that does not require generation of the constraint such as PostgreSQL. The mechanics of naming conventions for these particular constraints has been reorganized such that the naming determination is done at DDL compile time, rather than at constraint/table construction time.

  References: #3067

- [sql] [bug]

  Fixed bug in common table expressions whereby positional bound parameters could be expressed in the wrong final order when CTEs were nested in certain ways.

  References: #3090

- [sql] [bug]

  Fixed bug where multi-valued `Insert` construct would fail to check subsequent values entries beyond the first one given for literal SQL expressions.

  References: #3069

- [sql] [bug]

  Added a “str()” step to the dialect_kwargs iteration for Python version < 2.6.5, working around the “no unicode keyword arg” bug as these args are passed along as keyword args within some reflection processes.

  References: #3123

- [sql] [bug]

  The `TypeEngine.with_variant()` method will now accept a type class as an argument which is internally converted to an instance, using the same convention long established by other constructs such as `Column`.

  References: #3122

### postgresql

- [postgresql] [feature]

  Added kw argument `postgresql_regconfig` to the `ColumnOperators.match()` operator, allows the “reg config” argument to be specified to the `to_tsquery()` function emitted. Pull request courtesy Jonathan Vanasco.

  References: #3078

- [postgresql] [feature]

  Added support for PostgreSQL JSONB via `JSONB`. Pull request courtesy Damian Dimmich.

- [postgresql] [bug] [pg8000]

  Fixed bug introduced in 0.9.5 by new pg8000 isolation level feature where engine-level isolation level parameter would raise an error on connect.

  References: #3134

### mysql

- [mysql] [bug]

  MySQL error 2014 “commands out of sync” appears to be raised as a ProgrammingError, not OperationalError, in modern MySQL-Python versions; all MySQL error codes that are tested for “is disconnect” are now checked within OperationalError and ProgrammingError regardless.

  This change is also backported to: 0.8.7

  References: #3101

### sqlite

- [sqlite] [bug]

  Fixed a SQLite join rewriting issue where a subquery that is embedded as a scalar subquery such as within an IN would receive inappropriate substitutions from the enclosing query, if the same table were present inside the subquery as were in the enclosing query such as in a joined inheritance scenario.

  References: #3130

### mssql

- [mssql] [feature]

  Enabled “multivalues insert” for SQL Server 2008. Pull request courtesy Albert Cervin. Also expanded the checks for “IDENTITY INSERT” mode to include when the identity key is present in the VALUEs clause of the statement.

- [mssql] [bug]

  Added statement encoding to the “SET IDENTITY_INSERT” statements which operate when an explicit INSERT is being interjected into an IDENTITY column, to support non-ascii table identifiers on drivers such as pyodbc + unix + py2k that don’t support unicode statements.

  This change is also backported to: 0.8.7

- [mssql] [bug]

  In the SQL Server pyodbc dialect, repaired the implementation for the `description_encoding` dialect parameter, which when not explicitly set was preventing cursor.description from being parsed correctly in the case of result sets that contained names in alternate encodings. This parameter shouldn’t be needed going forward.

  This change is also backported to: 0.8.7

  References: #3091

- [mssql] [bug]

  Fixed a regression from 0.9.5 caused by #3025 where the query used to determine “default schema” is invalid in SQL Server 2000. For SQL Server 2000 we go back to defaulting to the “schema name” parameter of the dialect, which is configurable but defaults to ‘dbo’.

  References: #3025

### oracle

- [oracle] [bug] [tests]

  Fixed bug in oracle dialect test suite where in one test, ‘username’ was assumed to be in the database URL, even though this might not be the case.

  References: #3128

### tests

- [tests] [bug]

  Fixed bug where “python setup.py test” wasn’t calling into distutils appropriately, and errors would be emitted at the end of the test suite.

### misc

- [bug] [declarative]

  Fixed bug when the declarative `__abstract__` flag was not being distinguished for when it was actually the value `False`. The `__abstract__` flag needs to actually evaluate to a True value at the level being tested.

  References: #3097

## 0.9.6

Released: June 23, 2014

### orm

- [orm] [bug]

  Reverted the change for #3060 - this is a unit of work fix that is updated more comprehensively in 1.0 via #3061. The fix in #3060 unfortunately produces a new issue whereby an eager load of a many-to-one attribute can produce an event that is interpreted into an attribute change.

  References: #3060

## 0.9.5

Released: June 23, 2014

### orm

- [orm] [feature]

  The “primaryjoin” model has been stretched a bit further to allow a join condition that is strictly from a single column to itself, translated through some kind of SQL function or expression. This is kind of experimental, but the first proof of concept is a “materialized path” join condition where a path string is compared to itself using “like”. The `ColumnOperators.like()` operator has also been added to the list of valid operators to use in a primaryjoin condition.

  References: #3029

- [orm] [feature]

  Added new utility function `make_transient_to_detached()` which can be used to manufacture objects that behave as though they were loaded from a session, then detached. Attributes that aren’t present are marked as expired, and the object can be added to a Session where it will act like a persistent one.

  References: #3017

- [orm] [bug]

  Fixed bug in subquery eager loading where a long chain of eager loads across a polymorphic-subclass boundary in conjunction with polymorphic loading would fail to locate the subclass-link in the chain, erroring out with a missing property name on an `AliasedClass`.

  This change is also backported to: 0.8.7

  References: #3055

- [orm] [bug]

  Fixed ORM bug where the `class_mapper()` function would mask AttributeErrors or KeyErrors that should raise during mapper configuration due to user errors. The catch for attribute/keyerror has been made more specific to not include the configuration step.

  This change is also backported to: 0.8.7

  References: #3047

- [orm] [bug]

  Additional checks have been added for the case where an inheriting mapper is implicitly combining one of its column-based attributes with that of the parent, where those columns normally don’t necessarily share the same value. This is an extension of an existing check that was added via #1892; however this new check emits only a warning, instead of an exception, to allow for applications that may be relying upon the existing behavior.

  See also

  I’m getting a warning or error about “Implicitly combining column X under attribute Y”

  References: #3042

- [orm] [bug]

  Modified the behavior of `load_only()` such that primary key columns are always added to the list of columns to be “undeferred”; otherwise, the ORM can’t load the row’s identity. Apparently, one can defer the mapped primary keys and the ORM will fail, that hasn’t been changed. But as load_only is essentially saying “defer all but X”, it’s more critical that PK cols not be part of this deferral.

  References: #3080

- [orm] [bug]

  Fixed a few edge cases which arise in the so-called “row switch” scenario, where an INSERT/DELETE can be turned into an UPDATE. In this situation, a many-to-one relationship set to None, or in some cases a scalar attribute set to None, may not be detected as a net change in value, and therefore the UPDATE would not reset what was on the previous row. This is due to some as-yet unresolved side effects of the way attribute history works in terms of implicitly assuming None isn’t really a “change” for a previously un-set attribute. See also #3061.

  Note

  This change has been REVERTED in 0.9.6. The full fix will be in version 1.0 of SQLAlchemy.

  References: #3060

- [orm] [bug]

  Related to #3060, an adjustment has been made to the unit of work such that loading for related many-to-one objects is slightly more aggressive, in the case of a graph of self-referential objects that are to be deleted; the load of related objects is to help determine the correct order for deletion if passive_deletes is not set.

- [orm] [bug]

  Fixed bug in SQLite join rewriting where anonymized column names due to repeats would not correctly be rewritten in subqueries. This would affect SELECT queries with any kind of subquery + join.

  References: #3057

- [orm] [bug] [sql]

  Fixes to the newly enhanced boolean coercion in #2804 where the new rules for “where” and “having” wouldn’t take effect for the “whereclause” and “having” kw arguments of the `select()` construct, which is also what `Query` uses so wasn’t working in the ORM either.

  References: #3013

### examples

- [examples] [feature]

  Added a new example illustrating materialized paths, using the latest relationship features. Example courtesy Jack Zhou.

### engine

- [engine] [bug]

  Fixed bug which would occur if a DBAPI exception occurs when the engine first connects and does its initial checks, and the exception is not a disconnect exception, yet the cursor raises an error when we try to close it. In this case the real exception would be quashed as we tried to log the cursor close exception via the connection pool and failed, as we were trying to access the pool’s logger in a way that is inappropriate in this very specific scenario.

  References: #3063

- [engine] [bug]

  Fixed some “double invalidate” situations were detected where a connection invalidation could occur within an already critical section like a connection.close(); ultimately, these conditions are caused by the change in #2907, in that the “reset on return” feature calls out to the Connection/Transaction in order to handle it, where “disconnect detection” might be caught. However, it’s possible that the more recent change in #2985 made it more likely for this to be seen as the “connection invalidate” operation is much quicker, as the issue is more reproducible on 0.9.4 than 0.9.3.

  Checks are now added within any section that an invalidate might occur to halt further disallowed operations on the invalidated connection. This includes two fixes both at the engine level and at the pool level. While the issue was observed with highly concurrent gevent cases, it could in theory occur in any kind of scenario where a disconnect occurs within the connection close operation.

  References: #3043

### sql

- [sql] [feature]

  Liberalized the contract for `Index` a bit in that you can specify a `text()` expression as the target; the index no longer needs to have a table-bound column present if the index is to be manually added to the table, either via inline declaration or via `Table.append_constraint()`.

  References: #3028

- [sql] [feature]

  Added new flag `between.symmetric`, when set to True renders “BETWEEN SYMMETRIC”. Also added a new negation operator “notbetween_op”, which now allows an expression like `~col.between(x, y)` to render as “col NOT BETWEEN x AND y”, rather than a parenthesized NOT string.

  References: #2990

- [sql] [bug]

  Fixed bug in INSERT..FROM SELECT construct where selecting from a UNION would wrap the union in an anonymous (e.g. unlabeled) subquery.

  This change is also backported to: 0.8.7

  References: #3044

- [sql] [bug]

  Fixed bug where `Table.update()` and `Table.delete()` would produce an empty WHERE clause when an empty `and_()` or `or_()` or other blank expression were applied. This is now consistent with that of `select()`.

  This change is also backported to: 0.8.7

  References: #3045

- [sql] [bug]

  The `Column.nullable` flag is implicitly set to `False` when that `Column` is referred to in an explicit `PrimaryKeyConstraint` for that table. This behavior now matches that of when the `Column` itself has the `Column.primary_key` flag set to `True`, which is intended to be an exactly equivalent case.

  References: #3023

- [sql] [bug]

  Fixed bug where the `Operators.__and__()`, `Operators.__or__()` and `Operators.__invert__()` operator overload methods could not be overridden within a custom `Comparator` implementation.

  References: #3012

- [sql] [bug]

  Fixed bug in new `DialectKWArgs.argument_for()` method where adding an argument for a construct not previously included for any special arguments would fail.

  References: #3024

- [sql] [bug]

  Fixed regression introduced in 0.9 where new “ORDER BY <labelname>” feature from #1068 would not apply quoting rules to the label name as rendered in the ORDER BY.

  References: #1068, #3020

- [sql] [bug]

  Restored the import for `Function` to the `sqlalchemy.sql.expression` import namespace, which was removed at the beginning of 0.9.

### postgresql

- [postgresql] [feature]

  Added support for AUTOCOMMIT isolation level when using the pg8000 DBAPI. Pull request courtesy Tony Locke.

- [postgresql] [feature]

  Added a new flag `ARRAY.zero_indexes` to the PostgreSQL `ARRAY` type. When set to `True`, a value of one will be added to all array index values before passing to the database, allowing better interoperability between Python style zero-based indexes and PostgreSQL one-based indexes. Pull request courtesy Alexey Terentev.

  References: #2785

- [postgresql] [bug]

  Added the `hashable=False` flag to the PG `HSTORE` type, which is needed to allow the ORM to skip over trying to “hash” an ORM-mapped HSTORE column when requesting it in a mixed column/entity list. Patch courtesy Gunnlaugur Þór Briem.

  This change is also backported to: 0.8.7

  References: #3053

- [postgresql] [bug]

  Added a new “disconnect” message “connection has been closed unexpectedly”. This appears to be related to newer versions of SSL. Pull request courtesy Antti Haapala.

  This change is also backported to: 0.8.7

- [postgresql] [bug]

  The psycopg2 `.closed` accessor is now consulted when determining if an exception is a “disconnect” error; ideally, this should remove the need for any other inspection of the exception message to detect disconnect, however we will leave those existing messages in place as a fallback. This should be able to handle newer cases like “SSL EOF” conditions. Pull request courtesy Dirk Mueller.

  References: #3021

- [postgresql] [enhancement]

  Added a new type `OID` to the PostgreSQL dialect. While “oid” is generally a private type within PG that is not exposed in modern versions, there are some PG use cases such as large object support where these types might be exposed, as well as within some user-reported schema reflection use cases.

  References: #3002

### mysql

- [mysql] [bug]

  Fixed bug where column names added to `mysql_length` parameter on an index needed to have the same quoting for quoted names in order to be recognized. The fix makes the quotes optional but also provides the old behavior for backwards compatibility with those using the workaround.

  This change is also backported to: 0.8.7

  References: #3085

- [mysql] [bug]

  Added support for reflecting tables where an index includes KEY_BLOCK_SIZE using an equal sign. Pull request courtesy Sean McGivern.

  This change is also backported to: 0.8.7

### mssql

- [mssql] [bug]

  Revised the query used to determine the current default schema name to use the `database_principal_id()` function in conjunction with the `sys.database_principals` view so that we can determine the default schema independently of the type of login in progress (e.g., SQL Server, Windows, etc).

  References: #3025

### firebird

- [firebird] [bug]

  Fixed bug where the combination of “limit” rendering as “SELECT FIRST n ROWS” using a bound parameter (only firebird has both), combined with column-level subqueries which also feature “limit” as well as “positional” bound parameters (e.g. qmark style) would erroneously assign the subquery-level positions before that of the enclosing SELECT, thus returning parameters which are out of order.

  References: #3038

### tests

- [tests] [bug] [py3k]

  Corrected for some deprecation warnings involving the `imp` module and Python 3.3 or greater, when running tests. Pull request courtesy Matt Chisholm.

  References: #2830

### misc

- [bug] [declarative]

  The `__mapper_args__` dictionary is copied from a declarative mixin or abstract class when accessed, so that modifications made to this dictionary by declarative itself won’t conflict with that of other mappings. The dictionary is modified regarding the `version_id_col` and `polymorphic_on` arguments, replacing the column within with the one that is officially mapped to the local class/table.

  This change is also backported to: 0.8.7

  References: #3062

- [bug] [ext]

  Fixed bug in mutable extension where `MutableDict` did not report change events for the `setdefault()` dictionary operation.

  This change is also backported to: 0.8.7

  References: #3051, #3093

- [bug] [ext]

  Fixed bug where `MutableDict.setdefault()` didn’t return the existing or new value (this bug was not released in any 0.8 version). Pull request courtesy Thomas Hervé.

  This change is also backported to: 0.8.7

  References: #3051, #3093

- [bug] [testsuite]

  In public test suite, changed to use of `String(40)` from less-supported `Text` in `StringTest.test_literal_backslashes`. Pullreq courtesy Jan.

## 0.9.4

Released: March 28, 2014

### general

- [general] [feature]

  Support has been added for pytest to run tests. This runner is currently being supported in addition to nose, and will likely be preferred to nose going forward. The nose plugin system used by SQLAlchemy has been split out so that it works under pytest as well. There are no plans to drop support for nose at the moment and we hope that the test suite itself can continue to remain as agnostic of testing platform as possible. See the file README.unittests.rst for updated information on running tests with pytest.

  The test plugin system has also been enhanced to support running tests against multiple database URLs at once, by specifying the `--db` and/or `--dburi` flags multiple times. This does not run the entire test suite for each database, but instead allows test cases that are specific to certain backends make use of that backend as the test is run. When using pytest as the test runner, the system will also run specific test suites multiple times, once for each database, particularly those tests within the “dialect suite”. The plan is that the enhanced system will also be used by Alembic, and allow Alembic to run migration operation tests against multiple backends in one run, including third-party backends not included within Alembic itself. Third party dialects and extensions are also encouraged to standardize on SQLAlchemy’s test suite as a basis; see the file README.dialects.rst for background on building out from SQLAlchemy’s test platform.

- [general] [bug]

  Adjusted `setup.py` file to support the possible future removal of the `setuptools.Feature` extension from setuptools. If this keyword isn’t present, the setup will still succeed with setuptools rather than falling back to distutils. C extension building can be disabled now also by setting the DISABLE_SQLALCHEMY_CEXT environment variable. This variable works whether or not setuptools is even available.

  This change is also backported to: 0.8.6

  References: #2986

- [general] [bug]

  Fixed some test/feature failures occurring in Python 3.4, in particular the logic used to wrap “column default” callables wouldn’t work properly for Python built-ins.

  References: #2979

### orm

- [orm] [feature]

  Added new parameter `mapper.confirm_deleted_rows`. Defaults to True, indicates that a series of DELETE statements should confirm that the cursor rowcount matches the number of primary keys that should have matched; this behavior had been taken off in most cases (except when version_id is used) to support the unusual edge case of self-referential ON DELETE CASCADE; to accommodate this, the message is now just a warning, not an exception, and the flag can be used to indicate a mapping that expects self-referential cascaded deletes of this nature. See also #2403 for background on the original change.

  References: #3007

- [orm] [feature]

  A warning is emitted if the `MapperEvents.before_configured()` or `MapperEvents.after_configured()` events are applied to a specific mapper or mapped class, as the events are only invoked for the `Mapper` target at the general level.

- [orm] [feature]

  Added a new keyword argument `once=True` to `listen()` and `listens_for()`. This is a convenience feature which will wrap the given listener such that it is only invoked once.

- [orm] [feature]

  Added a new option to `relationship.innerjoin` which is to specify the string `"nested"`. When set to `"nested"` as opposed to `True`, the “chaining” of joins will parenthesize the inner join on the right side of an existing outer join, instead of chaining as a string of outer joins. This possibly should have been the default behavior when 0.9 was released, as we introduced the feature of right-nested joins in the ORM, however we are keeping it as a non-default for now to avoid further surprises.

  See also

  Right-nested inner joins available in joined eager loads

  References: #2976

- [orm] [bug]

  Fixed ORM bug where changing the primary key of an object, then marking it for DELETE would fail to target the correct row for DELETE.

  This change is also backported to: 0.8.6

  References: #3006

- [orm] [bug]

  Fixed regression from 0.8.3 as a result of #2818 where `Query.exists()` wouldn’t work on a query that only had a `Query.select_from()` entry but no other entities.

  This change is also backported to: 0.8.6

  References: #2995

- [orm] [bug]

  Improved an error message which would occur if a query() were made against a non-selectable, such as a `literal_column()`, and then an attempt was made to use `Query.join()` such that the “left” side would be determined as `None` and then fail. This condition is now detected explicitly.

  This change is also backported to: 0.8.6

- [orm] [bug]

  Removed stale names from `sqlalchemy.orm.interfaces.__all__` and refreshed with current names, so that an `import *` from this module again works.

  This change is also backported to: 0.8.6

  References: #2975

- [orm] [bug]

  Fixed a very old behavior where the lazy load emitted for a one-to-many could inappropriately pull in the parent table, and also return results inconsistent based on what’s in the parent table, when the primaryjoin includes some kind of discriminator against the parent table, such as `and_(parent.id == child.parent_id, parent.deleted == False)`. While this primaryjoin doesn’t make that much sense for a one-to-many, it is slightly more common when applied to the many-to-one side, and the one-to-many comes as a result of a backref. Loading rows from `child` in this case would keep `parent.deleted == False` as is within the query, thereby yanking it into the FROM clause and doing a cartesian product. The new behavior will now substitute the value of the local “parent.deleted” for that parameter as is appropriate. Though typically, a real-world app probably wants to use a different primaryjoin for the o2m side in any case.

  References: #2948

- [orm] [bug]

  Improved the check for “how to join from A to B” such that when a table has multiple, composite foreign keys targeting a parent table, the `relationship.foreign_keys` argument will be properly interpreted in order to resolve the ambiguity; previously this condition would raise that there were multiple FK paths when in fact the foreign_keys argument should be establishing which one is expected.

  References: #2965

- [orm] [bug]

  Added support for the not-quite-yet-documented `insert=True` flag for `listen()` to work with mapper / instance events.

- [orm] [bug] [engine]

  Fixed bug where events set to listen at the class level (e.g. on the `Mapper` or `ClassManager` level, as opposed to on an individual mapped class, and also on `Connection`) that also made use of internal argument conversion (which is most within those categories) would fail to be removable.

  References: #2973

- [orm] [bug]

  Fixed regression from 0.8 where using an option like `lazyload()` with the “wildcard” expression, e.g. `"*"`, would raise an assertion error in the case where the query didn’t contain any actual entities. This assertion is meant for other cases and was catching this one inadvertently.

- [orm] [bug] [sqlite]

  More fixes to SQLite “join rewriting”; the fix from #2967 implemented right before the release of 0.9.3 affected the case where a UNION contained nested joins in it. “Join rewriting” is a feature with a wide range of possibilities and is the first intricate “SQL rewriting” feature we’ve introduced in years, so we’re sort of going through a lot of iterations with it (not unlike eager loading back in the 0.2/0.3 series, polymorphic loading in 0.4/0.5). We should be there soon so thanks for bearing with us :).

  References: #2969

### examples

- [examples] [bug]

  Fixed bug in the versioned_history example where column-level INSERT defaults would prevent history values of NULL from being written.

### engine

- [engine] [feature]

  Added some new event mechanics for dialect-level events; the initial implementation allows an event handler to redefine the specific mechanics by which an arbitrary dialect invokes execute() or executemany() on a DBAPI cursor. The new events, at this point semi-public and experimental, are in support of some upcoming transaction-related extensions.

- [engine] [feature]

  An event listener can now be associated with a `Engine`, after one or more `Connection` objects have been created (such as by an orm `Session` or via explicit connect) and the listener will pick up events from those connections. Previously, performance concerns pushed the event transfer from `Engine` to `Connection` at init-time only, but we’ve inlined a bunch of conditional checks to make this possible without any additional function calls.

  References: #2978

- [engine] [bug]

  A major improvement made to the mechanics by which the `Engine` recycles the connection pool when a “disconnect” condition is detected; instead of discarding the pool and explicitly closing out connections, the pool is retained and a “generational” timestamp is updated to reflect the current time, thereby causing all existing connections to be recycled when they are next checked out. This greatly simplifies the recycle process, removes the need for “waking up” connect attempts waiting on the old pool and eliminates the race condition that many immediately-discarded “pool” objects could be created during the recycle operation.

  References: #2985

- [engine] [bug]

  The `ConnectionEvents.after_cursor_execute()` event is now emitted for the “_cursor_execute()” method of `Connection`; this is the “quick” executor that is used for things like when a sequence is executed ahead of an INSERT statement, as well as for dialect startup checks like unicode returns, charset, etc. the `ConnectionEvents.before_cursor_execute()` event was already invoked here. The “executemany” flag is now always set to False here, as this event always corresponds to a single execution. Previously the flag could be True if we were acting on behalf of an executemany INSERT statement.

### sql

- [sql] [feature]

  Added support for literal rendering of boolean values, e.g. “true” / “false” or “1” / “0”.

- [sql] [feature]

  Added a new feature `conv()`, the purpose of which is to mark a constraint name as already having had a naming convention applied. This token will be used by Alembic migrations as of Alembic 0.6.4 in order to render constraints in migration scripts with names marked as already having been subject to a naming convention.

- [sql] [feature]

  The new dialect-level keyword argument system for schema-level constructs has been enhanced in order to assist with existing schemes that rely upon addition of ad-hoc keyword arguments to constructs.

  E.g., a construct such as `Index` will again accept ad-hoc keyword arguments within the `Index.kwargs` collection, after construction:

      idx = Index("a", "b")
      idx.kwargs["mysql_someargument"] = True

  To suit the use case of allowing custom arguments at construction time, the `DialectKWArgs.argument_for()` method now allows this registration:

      Index.argument_for("mysql", "someargument", False)

      idx = Index("a", "b", mysql_someargument=True)

  See also

  `DialectKWArgs.argument_for()`

  References: #2866, #2962

- [sql] [bug]

  Fixed bug in `tuple_()` construct where the “type” of essentially the first SQL expression would be applied as the “comparison type” to a compared tuple value; this has the effect in some cases of an inappropriate “type coercion” occurring, such as when a tuple that has a mix of String and Binary values improperly coerces target values to Binary even though that’s not what they are on the left side. `tuple_()` now expects heterogeneous types within its list of values.

  This change is also backported to: 0.8.6

  References: #2977

- [sql] [bug]

  Fixed an 0.9 regression where a `Table` that failed to reflect correctly wouldn’t be removed from the parent `MetaData`, even though in an invalid state. Pullreq courtesy Roman Podoliaka.

  References: #2988

- [sql] [bug]

  `MetaData.naming_convention` feature will now also apply to `CheckConstraint` objects that are associated directly with a `Column` instead of just on the `Table`.

- [sql] [bug]

  Fixed bug in new `MetaData.naming_convention` feature where the name of a check constraint making use of the “%(constraint_name)s” token would get doubled up for the constraint generated by a boolean or enum type, and overall duplicate events would cause the “%(constraint_name)s” token to keep compounding itself.

  References: #2991

- [sql] [bug]

  Adjusted the logic which applies names to the .c collection when a no-name `BindParameter` is received, e.g. via `literal()` or similar; the “key” of the bind param is used as the key within .c. rather than the rendered name. Since these binds have “anonymous” names in any case, this allows individual bound parameters to have their own name within a selectable if they are otherwise unlabeled.

  References: #2974

- [sql] [bug]

  Some changes to how the `FromClause.c` collection behaves when presented with duplicate columns. The behavior of emitting a warning and replacing the old column with the same name still remains to some degree; the replacement in particular is to maintain backwards compatibility. However, the replaced column still remains associated with the `c` collection now in a collection `._all_columns`, which is used by constructs such as aliases and unions, to deal with the set of columns in `c` more towards what is actually in the list of columns rather than the unique set of key names. This helps with situations where SELECT statements with same-named columns are used in unions and such, so that the union can match the columns up positionally and also there’s some chance of `FromClause.corresponding_column()` still being usable here (it can now return a column that is only in selectable.c._all_columns and not otherwise named). The new collection is underscored as we still need to decide where this list might end up. Theoretically it would become the result of iter(selectable.c), however this would mean that the length of the iteration would no longer match the length of keys(), and that behavior needs to be checked out.

  References: #2974

- [sql] [bug]

  Fixed issue in new `TextClause.columns()` method where the ordering of columns given positionally would not be preserved. This could have potential impact in positional situations such as applying the resulting `TextAsFrom` object to a union.

### postgresql

- [postgresql] [feature]

  Enabled “sane multi-row count” checking for the psycopg2 DBAPI, as this seems to be supported as of psycopg2 2.0.9.

  This change is also backported to: 0.8.6

- [postgresql] [bug]

  Fixed regression caused by release 0.8.5 / 0.9.3’s compatibility enhancements where index reflection on PostgreSQL versions specific to only the 8.1, 8.2 series again broke, surrounding the ever problematic int2vector type. While int2vector supports array operations as of 8.1, apparently it only supports CAST to a varchar as of 8.3.

  This change is also backported to: 0.8.6

  References: #3000

### mysql

- [mysql] [bug]

  Tweaked the settings for mysql-connector-python; in Py2K, the “supports unicode statements” flag is now False, so that SQLAlchemy will encode the SQL string (note: not the parameters) to bytes before sending to the database. This seems to allow all unicode-related tests to pass for mysql-connector, including those that use non-ascii table/column names, as well as some tests for the TEXT type using unicode under cursor.executemany().

### oracle

- [oracle] [feature]

  Added a new engine option `coerce_to_unicode=True` to the cx_Oracle dialect, which restores the cx_Oracle outputtypehandler approach to Python unicode conversion under Python 2, which was removed in 0.9.2 as a result of #2911. Some use cases would prefer that unicode coercion is unconditional for all string values, despite performance concerns. Pull request courtesy Christoph Zwerschke.

  References: #2911

- [oracle] [bug]

  Added new datatype `DATE`, which is a subclass of `DateTime`. As Oracle has no “datetime” type per se, it instead has only `DATE`, it is appropriate here that the `DATE` type as present in the Oracle dialect be an instance of `DateTime`. This issue doesn’t change anything as far as the behavior of the type, as data conversion is handled by the DBAPI in any case, however the improved subclass layout will help the use cases of inspecting types for cross-database compatibility. Also removed uppercase `DATETIME` from the Oracle dialect as this type isn’t functional in that context.

  References: #2987

### tests

- [tests] [bug]

  Fixed a few errant `u''` strings that would prevent tests from passing in Py3.2. Patch courtesy Arfrever Frehtes Taifersar Arahesis.

  References: #2980

### misc

- [bug] [ext]

  Fixed bug in mutable extension as well as `flag_modified()` where the change event would not be propagated if the attribute had been reassigned to itself.

  This change is also backported to: 0.8.6

  References: #2997

- [bug] [automap] [ext]

  Added support to automap for the case where a relationship should not be created between two classes that are in a joined inheritance relationship, for those foreign keys that link the subclass back to the superclass.

  References: #3004

- [bug] [pool]

  Fixed small issue in `SingletonThreadPool` where the current connection to be returned might get inadvertently cleaned out during the “cleanup” process. Patch courtesy jd23.

- [bug] [ext] [py3k]

  Fixed bug in association proxy where assigning an empty slice (e.g. `x[:] = [...]`) would fail on Py3k.

- [bug] [ext]

  Fixed a regression in association proxy caused by #2810 which caused a user-provided “getter” to no longer receive values of `None` when fetching scalar values from a target that is non-present. The check for None introduced by this change is now moved into the default getter, so a user-provided getter will also again receive values of None.

  References: #2810

## 0.9.3

Released: February 19, 2014

### orm

- [orm] [feature]

  Added new `MapperEvents.before_configured()` event which allows an event at the start of `configure_mappers()`, as well as `__declare_first__()` hook within declarative to complement `__declare_last__()`.

- [orm] [bug]

  Fixed bug where `Query.get()` would fail to consistently raise the `InvalidRequestError` that invokes when called on a query with existing criterion, when the given identity is already present in the identity map.

  This change is also backported to: 0.8.5

  References: #2951

- [orm] [bug] [sqlite]

  Fixed bug in SQLite “join rewriting” where usage of an exists() construct would fail to be rewritten properly, such as when the exists is mapped to a column_property in an intricate nested-join scenario. Also fixed a somewhat related issue where join rewriting would fail on the columns clause of the SELECT statement if the targets were aliased tables, as opposed to individual aliased columns.

  References: #2967

- [orm] [bug]

  Fixed an 0.9 regression where ORM instance or mapper events applied to a base class such as a declarative base with the propagate=True flag would fail to apply to existing mapped classes which also used inheritance due to an assertion. Additionally, repaired an attribute error which could occur during removal of such an event, depending on how it was first assigned.

  References: #2949

- [orm] [bug]

  Improved the initialization logic of composite attributes such that calling `MyClass.attribute` will not require that the configure mappers step has occurred, e.g. it will just work without throwing any error.

  References: #2935

- [orm] [bug]

  More issues with [ticket:2932] first resolved in 0.9.2 where using a column key of the form `<tablename>_<columnname>` matching that of an aliased column in the text would still not match at the ORM level, which is ultimately due to a core column-matching issue. Additional rules have been added so that the column `_label` is taken into account when working with a `TextAsFrom` construct or with literal columns.

  References: #2932

### orm declarative

- [orm] [declarative] [bug]

  Fixed bug where `AbstractConcreteBase` would fail to be fully usable within declarative relationship configuration, as its string classname would not be available in the registry of classnames at mapper configuration time. The class now explicitly adds itself to the class registry, and additionally both `AbstractConcreteBase` as well as `ConcreteBase` set themselves up before mappers are configured within the `configure_mappers()` setup, using the new `MapperEvents.before_configured()` event.

  References: #2950

### examples

- [examples] [feature]

  Added optional “changed” column to the versioned rows example, as well as support for when the versioned `Table` has an explicit `Table.schema` argument. Pull request courtesy jplaverdure.

### engine

- [engine] [bug] [pool]

  Fixed a critical regression caused by #2880 where the newly concurrent ability to return connections from the pool means that the “first_connect” event is now no longer synchronized either, thus leading to dialect mis-configurations under even minimal concurrency situations.

  This change is also backported to: 0.8.5

  References: #2880, #2964

### sql

- [sql] [bug]

  Fixed bug where calling `Insert.values()` with an empty list or tuple would raise an IndexError. It now produces an empty insert construct as would be the case with an empty dictionary.

  This change is also backported to: 0.8.5

  References: #2944

- [sql] [bug]

  Fixed bug where `ColumnOperators.in_()` would go into an endless loop if erroneously passed a column expression whose comparator included the `__getitem__()` method, such as a column that uses the `ARRAY` type.

  This change is also backported to: 0.8.5

  References: #2957

- [sql] [bug]

  Fixed regression in new “naming convention” feature where conventions would fail if the referred table in a foreign key contained a schema name. Pull request courtesy Thomas Farvour.

- [sql] [bug]

  Fixed bug where so-called “literal render” of `bindparam()` constructs would fail if the bind were constructed with a callable, rather than a direct value. This prevented ORM expressions from being rendered with the “literal_binds” compiler flag.

### postgresql

- [postgresql] [feature]

  Added the `TypeEngine.python_type` convenience accessor onto the `ARRAY` type. Pull request courtesy Alexey Terentev.

- [postgresql] [bug]

  Added an additional message to psycopg2 disconnect detection, “could not send data to server”, which complements the existing “could not receive data from server” and has been observed by users.

  This change is also backported to: 0.8.5

  References: #2936

- [postgresql] [bug]

  > Support has been improved for PostgreSQL reflection behavior on very old (pre 8.1) versions of PostgreSQL, and potentially other PG engines such as Redshift (assuming Redshift reports the version as < 8.1). The query for “indexes” as well as “primary keys” relies upon inspecting a so-called “int2vector” datatype, which refuses to coerce to an array prior to 8.1 causing failures regarding the “ANY()” operator used in the query. Extensive googling has located the very hacky, but recommended-by-PG-core-developer query to use when PG version < 8.1 is in use, so index and primary key constraint reflection now work on these versions.

  This change is also backported to: 0.8.5

- [postgresql] [bug]

  Revised this very old issue where the PostgreSQL “get primary key” reflection query were updated to take into account primary key constraints that were renamed; the newer query fails on very old versions of PostgreSQL such as version 7, so the old query is restored in those cases when server_version_info < (8, 0) is detected.

  This change is also backported to: 0.8.5

  References: #2291

- [postgresql] [bug]

  Added server version detection to the newly added dialect startup query for “show standard_conforming_strings”; as this variable was added as of PG 8.2, we skip the query for PG versions who report a version string earlier than that.

  References: #2946

### mysql

- [mysql] [feature]

  Added new MySQL-specific `DATETIME` which includes fractional seconds support; also added fractional seconds support to `TIMESTAMP`. DBAPI support is limited, though fractional seconds are known to be supported by MySQL Connector/Python. Patch courtesy Geert JM Vanderkelen.

  This change is also backported to: 0.8.5

  References: #2941

- [mysql] [bug]

  Added support for the `PARTITION BY` and `PARTITIONS` MySQL table keywords, specified as `mysql_partition_by='value'` and `mysql_partitions='value'` to `Table`. Pull request courtesy Marcus McCurdy.

  This change is also backported to: 0.8.5

  References: #2966

- [mysql] [bug]

  Fixed bug which prevented MySQLdb-based dialects (e.g. pymysql) from working in Py3K, where a check for “connection charset” would fail due to Py3K’s more strict value comparison rules. The call in question wasn’t taking the database version into account in any case as the server version was still None at that point, so the method overall has been simplified to rely upon connection.character_set_name().

  This change is also backported to: 0.8.5

  References: #2933

- [mysql] [bug] [cymysql]

  Fixed bug in cymysql dialect where a version string such as `'33a-MariaDB'` would fail to parse properly. Pull request courtesy Matt Schmidt.

  References: #2934

### sqlite

- [sqlite] [bug]

  The SQLite dialect will now skip unsupported arguments when reflecting types; such as if it encounters a string like `INTEGER(5)`, the `INTEGER` type will be instantiated without the “5” being included, based on detecting a `TypeError` on the first attempt.

- [sqlite] [bug]

  Support has been added to SQLite type reflection to fully support the “type affinity” contract specified at https://www.sqlite.org/datatype3.html. In this scheme, keywords like `INT`, `CHAR`, `BLOB` or `REAL` located in the type name generically associate the type with one of five affinities. Pull request courtesy Erich Blume.

  See also

  Type Reflection

### misc

- [bug] [ext]

  Fixed bug where the `AutomapBase` class of the new automap extension would fail if classes were pre-arranged in single or potentially joined inheritance patterns. The repaired joined inheritance issue could also potentially apply when using `DeferredReflection` as well.

## 0.9.2

Released: February 2, 2014

### orm

- [orm] [feature]

  Added a new parameter `Operators.op.is_comparison`. This flag allows a custom op from `Operators.op()` to be considered as a “comparison” operator, thus usable for custom `relationship.primaryjoin` conditions.

  See also

  Using custom operators in join conditions

- [orm] [feature]

  Support is improved for supplying a `join()` construct as the target of `relationship.secondary` for the purposes of creating very complex `relationship()` join conditions. The change includes adjustments to query joining, joined eager loading to not render a SELECT subquery, changes to lazy loading such that the “secondary” target is properly included in the SELECT, and changes to declarative to better support specification of a join() object with classes as targets.

  The new use case is somewhat experimental, but a new documentation section has been added.

  See also

  Composite “Secondary” Joins

- [orm] [bug]

  Fixed error message when an iterator object is passed to `class_mapper()` or similar, where the error would fail to render on string formatting. Pullreq courtesy Kyle Stark.

  This change is also backported to: 0.8.5

- [orm] [bug]

  Fixed bug in new `TextAsFrom` construct where `Column`- oriented row lookups were not matching up to the ad-hoc `ColumnClause` objects that `TextAsFrom` generates, thereby making it not usable as a target in `Query.from_statement()`. Also fixed `Query.from_statement()` mechanics to not mistake a `TextAsFrom` for a `Select` construct. This bug is also an 0.9 regression as the `TextClause.columns()` method is called to accommodate the `text.typemap` argument.

  References: #2932

- [orm] [bug]

  Added a new directive used within the scope of an attribute “set” operation to disable autoflush, in the case that the attribute needs to lazy-load the “old” value, as in when replacing one-to-one values or some kinds of many-to-one. A flush at this point otherwise occurs at the point that the attribute is None and can cause NULL violations.

  References: #2921

- [orm] [bug]

  Fixed an 0.9 regression where the automatic aliasing applied by `Query` and in other situations where selects or joins were aliased (such as joined table inheritance) could fail if a user-defined `Column` subclass were used in the expression. In this case, the subclass would fail to propagate ORM-specific “annotations” along needed by the adaptation. The “expression annotations” system has been corrected to account for this case.

  References: #2918

- [orm] [bug]

  Fixed a bug involving the new flattened JOIN structures which are used with `joinedload()` (thereby causing a regression in joined eager loading) as well as `aliased()` in conjunction with the `flat=True` flag and joined-table inheritance; basically multiple joins across a “parent JOIN sub” entity using different paths to get to a target class wouldn’t form the correct ON conditions. An adjustment / simplification made in the mechanics of figuring out the “left side” of the join in the case of an aliased, joined-inh class repairs the issue.

  References: #2908

### examples

- [examples] [bug]

  Added a tweak to the “history_meta” example where the check for “history” on a relationship-bound attribute will now no longer emit any SQL if the relationship is unloaded.

### engine

- [engine] [feature] [pool]

  Added a new pool event `PoolEvents.invalidate()`. Called when a DBAPI connection is to be marked as “invalidated” and discarded from the pool.

### sql

- [sql] [feature]

  Added `MetaData.reflect.dialect_kwargs` to support dialect-level reflection options for all `Table` objects reflected.

- [sql] [feature]

  Added a new feature which allows automated naming conventions to be applied to `Constraint` and `Index` objects. Based on a recipe in the wiki, the new feature uses schema-events to set up names as various schema objects are associated with each other. The events then expose a configuration system through a new argument `MetaData.naming_convention`. This system allows production of both simple and custom naming schemes for constraints and indexes on a per-`MetaData` basis.

  See also

  Configuring Constraint Naming Conventions

  References: #2923

- [sql] [feature]

  Options can now be specified on a `PrimaryKeyConstraint` object independently of the specification of columns in the table with the `primary_key=True` flag; use a `PrimaryKeyConstraint` object with no columns in it to achieve this result.

  Previously, an explicit `PrimaryKeyConstraint` would have the effect of those columns marked as `primary_key=True` being ignored; since this is no longer the case, the `PrimaryKeyConstraint` will now assert that either one style or the other is used to specify the columns, or if both are present, that the column lists match exactly. If an inconsistent set of columns in the `PrimaryKeyConstraint` and within the `Table` marked as `primary_key=True` are present, a warning is emitted, and the list of columns is taken only from the `PrimaryKeyConstraint` alone as was the case in previous releases.

  See also

  `PrimaryKeyConstraint`

  References: #2910

- [sql] [feature]

  The system by which schema constructs and certain SQL constructs accept dialect-specific keyword arguments has been enhanced. This system includes commonly the `Table` and `Index` constructs, which accept a wide variety of dialect-specific arguments such as `mysql_engine` and `postgresql_where`, as well as the constructs `PrimaryKeyConstraint`, `UniqueConstraint`, `Update`, `Insert` and `Delete`, and also newly added kwarg capability to `ForeignKeyConstraint` and `ForeignKey`. The change is that participating dialects can now specify acceptable argument lists for these constructs, allowing an argument error to be raised if an invalid keyword is specified for a particular dialect. If the dialect portion of the keyword is unrecognized, a warning is emitted only; while the system will actually make use of setuptools entrypoints in order to locate non-local dialects, the use case where certain dialect-specific arguments are used in an environment where that third-party dialect is uninstalled remains supported. Dialects also have to explicitly opt-in to this system, so that external dialects which aren’t making use of this system will remain unaffected.

  References: #2866

- [sql] [bug]

  The behavior of `Table.tometadata()` has been adjusted such that the schema target of a `ForeignKey` will not be changed unless that schema matches that of the parent table. That is, if a table “schema_a.user” has a foreign key to “schema_b.order.id”, the “schema_b” target will be maintained whether or not the “schema” argument is passed to `Table.tometadata()`. However if a table “schema_a.user” refers to “schema_a.order.id”, the presence of “schema_a” will be updated on both the parent and referred tables. This is a behavioral change hence isn’t likely to be backported to 0.8; it is assumed that the previous behavior is pretty buggy however and that it’s unlikely anyone was relying upon it.

  Additionally, a new parameter has been added `Table.tometadata.referred_schema_fn`. This refers to a callable function which will be used to determine the new referred schema for any `ForeignKeyConstraint` encountered in the tometadata operation. This callable can be used to revert to the previous behavior or to customize how referred schemas are treated on a per-constraint basis.

  References: #2913

- [sql] [bug]

  Fixed bug whereby binary type would fail in some cases if used with a “test” dialect, such as a DefaultDialect or other dialect with no DBAPI.

- [sql] [bug] [py3k]

  Fixed bug where “literal binds” wouldn’t work with a bound parameter that’s a binary type. A similar, but different, issue is fixed in 0.8.

- [sql] [bug]

  Fixed regression whereby the “annotation” system used by the ORM was leaking into the names used by standard functions in `sqlalchemy.sql.functions`, such as `func.coalesce()` and `func.max()`. Using these functions in ORM attributes and thus producing annotated versions of them could corrupt the actual function name rendered in the SQL.

  References: #2927

- [sql] [bug]

  Fixed 0.9 regression where the new sortable support for `RowProxy` would lead to `TypeError` when compared to non-tuple types as it attempted to apply tuple() to the “other” object unconditionally. The full range of Python comparison operators have now been implemented on `RowProxy`, using an approach that guarantees a comparison system that is equivalent to that of a tuple, and the “other” object is only coerced if it’s an instance of RowProxy.

  References: #2848, #2924

- [sql] [bug]

  A `UniqueConstraint` created inline with a `Table` that has no columns within it will be skipped. Pullreq courtesy Derek Harland.

- [sql] [bug] [orm]

  Fixed the multiple-table “UPDATE..FROM” construct, only usable on MySQL, to correctly render the SET clause among multiple columns with the same name across tables. This also changes the name used for the bound parameter in the SET clause to “<tablename>_<colname>” for the non-primary table only; as this parameter is typically specified using the `Column` object directly this should not have an impact on applications. The fix takes effect for both `Table.update()` as well as `Query.update()` in the ORM.

  References: #2912

### schema

- [schema] [bug]

  Restored `sqlalchemy.schema.SchemaVisitor` to the `.schema` module. Pullreq courtesy Sean Dague.

### postgresql

- [postgresql] [feature]

  Added a new dialect-level argument `postgresql_ignore_search_path`; this argument is accepted by both the `Table` constructor as well as by the `MetaData.reflect()` method. When in use against PostgreSQL, a foreign-key referenced table which specifies a remote schema name will retain that schema name even if the name is present in the `search_path`; the default behavior since 0.7.3 has been that schemas present in `search_path` would not be copied to reflected `ForeignKey` objects. The documentation has been updated to describe in detail the behavior of the `pg_get_constraintdef()` function and how the `postgresql_ignore_search_path` feature essentially determines if we will honor the schema qualification reported by this function or not.

  See also

  Remote-Schema Table Introspection and PostgreSQL search_path

  References: #2922

### mysql

- [mysql] [bug]

  Some missing methods added to the cymysql dialect, including _get_server_version_info() and _detect_charset(). Pullreq courtesy Hajime Nakagami.

  This change is also backported to: 0.8.5

- [mysql] [bug] [sql]

  Added new test coverage for so-called “down adaptions” of SQL types, where a more specific type is adapted to a more generic one - this use case is needed by some third party tools such as `sqlacodegen`. The specific cases that needed repair within this test suite were that of `ENUM` being downcast into a `Enum`, and that of SQLite date types being cast into generic date types. The `adapt()` method needed to become more specific here to counteract the removal of a “catch all” `**kwargs` collection on the base `TypeEngine` class that was removed in 0.9.

  References: #2917

- [mysql] [bug]

  The MySQL CAST compilation now takes into account aspects of a string type such as “charset” and “collation”. While MySQL wants all character- based CAST calls to use the CHAR type, we now create a real CHAR object at CAST time and copy over all the parameters it has, so that an expression like `cast(x, mysql.TEXT(charset='utf8'))` will render `CAST(t.col AS CHAR CHARACTER SET utf8)`.

- [mysql] [bug]

  Added new “unicode returns” detection to the MySQL dialect and to the default dialect system overall, such that any dialect can add extra “tests” to the on-first-connect “does this DBAPI return unicode directly?” detection. In this case, we are adding a check specifically against the “utf8” encoding with an explicit “utf8_bin” collation type (after checking that this collation is available) to test for some buggy unicode behavior observed with MySQLdb version 1.2.3. While MySQLdb has resolved this issue as of 1.2.4, the check here should guard against regressions. The change also allows the “unicode” checks to log in the engine logs, which was not previously the case.

  References: #2906

- [mysql] [bug] [engine] [pool]

  `Connection` now associates a new `RootTransaction` or `TwoPhaseTransaction` with its immediate `_ConnectionFairy` as a “reset handler” for the span of that transaction, which takes over the task of calling commit() or rollback() for the “reset on return” behavior of `Pool` if the transaction was not otherwise completed. This resolves the issue that a picky transaction like that of MySQL two-phase will be properly closed out when the connection is closed without an explicit rollback or commit (e.g. no longer raises “XAER_RMFAIL” in this case - note this only shows up in logging as the exception is not propagated within pool reset). This issue would arise e.g. when using an orm `Session` with `twophase` set, and then `Session.close()` is called without an explicit rollback or commit. The change also has the effect that you will now see an explicit “ROLLBACK” in the logs when using a `Session` object in non-autocommit mode regardless of how that session was discarded. Thanks to Jeff Dairiki and Laurence Rowe for isolating the issue here.

  References: #2907

### sqlite

- [sqlite] [bug]

  Fixed bug whereby SQLite compiler failed to propagate compiler arguments such as “literal binds” into a CAST expression.

### mssql

- [mssql] [feature]

  Added an option `mssql_clustered` to the `UniqueConstraint` and `PrimaryKeyConstraint` constructs; on SQL Server, this adds the `CLUSTERED` keyword to the constraint construct within DDL. Pullreq courtesy Derek Harland.

### oracle

- [oracle] [bug]

  It’s been observed that the usage of a cx_Oracle “outputtypehandler” in Python 2.xx in order to coerce string values to Unicode is inordinately expensive; even though cx_Oracle is written in C, when you pass the Python `unicode` primitive to cursor.var() and associate with an output handler, the library counts every conversion as a Python function call with all the requisite overhead being recorded; this despite the fact when running in Python 3, all strings are also unconditionally coerced to unicode but it does not incur this overhead, meaning that cx_Oracle is failing to use performant techniques in Py2K. As SQLAlchemy cannot easily select for this style of type handler on a per-column basis, the handler was assembled unconditionally thereby adding the overhead to all string access.

  So this logic has been replaced with SQLAlchemy’s own unicode conversion system, which now only takes effect in Py2K for columns that are requested as unicode. When C extensions are used, SQLAlchemy’s system appears to be 2-3x faster than cx_Oracle’s. Additionally, SQLAlchemy’s unicode conversion has been enhanced such that when the “conditional” converter is required (now needed for the Oracle backend), the check for “already unicode” is now performed in C and no longer introduces significant overhead.

  This change has two impacts on the cx_Oracle backend. One is that string values in Py2K which aren’t specifically requested with the Unicode type or convert_unicode=True will now come back as `str`, not `unicode` - this behavior is similar to a backend such as MySQL. Additionally, when unicode values are requested with the cx_Oracle backend, if the C extensions are not used, there is now an additional overhead of an isinstance() check per column. This tradeoff has been made as it can be worked around and no longer places a performance burden on the likely majority of Oracle result columns that are non-unicode strings.

  References: #2911

### misc

- [bug] [pool]

  The argument names for the `PoolEvents.reset()` event have been renamed to `dbapi_connection` and `connection_record` in order to maintain consistency with all the other pool events. It is expected that any existing listeners for this relatively new and seldom-used event are using positional style to receive arguments in any case.

- [bug] [cextensions] [py3k]

  Fixed an issue where the C extensions in Py3K are using the wrong API to specify the top-level module function, which breaks in Python 3.4b2. Py3.4b2 changes PyMODINIT_FUNC to return “void” instead of `PyObject *`, so we now make sure to use “PyMODINIT_FUNC” instead of `PyObject *` directly. Pull request courtesy cgohlke.

## 0.9.1

Released: January 5, 2014

### orm

- [orm] [feature] [extensions]

  A new, experimental extension `sqlalchemy.ext.automap` is added. This extension expands upon the functionality of Declarative as well as the `DeferredReflection` class to produce a base class which automatically generates mapped classes and relationships based on table metadata.

  See also

  Automap Extension

  Automap

- [orm] [bug] [events]

  Fixed regression where using a `functools.partial()` with the event system would cause a recursion overflow due to usage of inspect.getargspec() on it in order to detect a legacy calling signature for certain events, and apparently there’s no way to do this with a partial object. Instead we skip the legacy check and assume the modern style; the check itself now only occurs for the SessionEvents.after_bulk_update and SessionEvents.after_bulk_delete events. Those two events will require the new signature style if assigned to a “partial” event listener.

  References: #2905

- [orm] [bug]

  Fixed bug where using new `Session.info` attribute would fail if the `.info` argument were only passed to the `sessionmaker` creation call but not to the object itself. Courtesy Robin Schoonover.

- [orm] [bug]

  Fixed regression where we don’t check the given name against the correct string class when setting up a backref based on a name, therefore causing the error “too many values to unpack”. This was related to the Py3k conversion.

  References: #2901

- [orm] [bug]

  Fixed regression where we apparently still create an implicit alias when saying query(B).join(B.cs), where “C” is a joined inh class; however, this implicit alias was created only considering the immediate left side, and not a longer chain of joins along different joined-inh subclasses of the same base. As long as we’re still implicitly aliasing in this case, the behavior is dialed back a bit so that it will alias the right side in a wider variety of cases.

  References: #2903

### orm declarative

- [orm] [declarative] [bug]

  Fixed an extremely unlikely memory issue where when using `DeferredReflection` to define classes pending for reflection, if some subset of those classes were discarded before the `DeferredReflection.prepare()` method were called to reflect and map the class, a strong reference to the class would remain held within the declarative internals. This internal collection of “classes to map” now uses weak references against the classes themselves.

- [orm] [declarative] [bug]

  A quasi-regression where apparently in 0.8 you can set a class-level attribute on declarative to simply refer directly to an `InstrumentedAttribute` on a superclass or on the class itself, and it acts more or less like a synonym; in 0.9, this fails to set up enough bookkeeping to keep up with the more liberalized backref logic from #2789. Even though this use case was never directly considered, it is now detected by declarative at the “setattr()” level as well as when setting up a subclass, and the mirrored/renamed attribute is now set up as a `synonym()` instead.

  References: #2900

### sql

- [sql] [feature]

  Conjunctions like `and_()` and `or_()` can now accept Python generators as a single argument, e.g.:

      and_(x == y for x, y in tuples)

  The logic here looks for a single argument `*args` where the first element is an instance of `types.GeneratorType`.

### schema

- [schema] [feature]

  The `Table.extend_existing` and `Table.autoload_replace` parameters are now available on the `MetaData.reflect()` method.

## 0.9.0

Released: December 30, 2013

### orm

- [orm] [feature]

  The `StatementError` or DBAPI-related subclass now can accommodate additional information about the “reason” for the exception; the `Session` now adds some detail to it when the exception occurs within an autoflush. This approach is taken as opposed to combining `FlushError` with a Python 3 style “chained exception” approach so as to maintain compatibility both with Py2K code as well as code that already catches `IntegrityError` or similar.

- [orm] [feature] [backrefs]

  Added new argument `include_backrefs=True` to the `validates()` function; when set to False, a validation event will not be triggered if the event was initiated as a backref to an attribute operation from the other side.

  See also

  include_backrefs=False option for @validates

  References: #1535

- [orm] [feature]

  A new API for specifying the `FOR UPDATE` clause of a `SELECT` is added with the new `Query.with_for_update()` method, to complement the new `GenerativeSelect.with_for_update()` method. Pull request courtesy Mario Lassnig.

  See also

  New FOR UPDATE support on select(), Query()

- [orm] [bug]

  An adjustment to the `subqueryload()` strategy which ensures that the query runs after the loading process has begun; this is so that the subqueryload takes precedence over other loaders that may be hitting the same attribute due to other eager/noload situations at the wrong time.

  This change is also backported to: 0.8.5

  References: #2887

- [orm] [bug]

  Fixed bug when using joined table inheritance from a table to a select/alias on the base, where the PK columns were also not same named; the persistence system would fail to copy primary key values from the base table to the inherited table upon INSERT.

  This change is also backported to: 0.8.5

  References: #2885

- [orm] [bug]

  `composite()` will raise an informative error message when the columns/attribute (names) passed don’t resolve to a Column or mapped attribute (such as an erroneous tuple); previously raised an unbound local.

  This change is also backported to: 0.8.5

  References: #2889

- [orm] [bug]

  Fixed a regression introduced by #2818 where the EXISTS query being generated would produce a “columns being replaced” warning for a statement with two same-named columns, as the internal SELECT wouldn’t have use_labels set.

  This change is also backported to: 0.8.4

  References: #2818

- [orm] [bug] [collections] [py3k]

  Added support for the Python 3 method `list.clear()` within the ORM collection instrumentation system; pull request courtesy Eduardo Schettino.

- [orm] [bug]

  Some refinements to the `AliasedClass` construct with regards to descriptors, like hybrids, synonyms, composites, user-defined descriptors, etc. The attribute adaptation which goes on has been made more robust, such that if a descriptor returns another instrumented attribute, rather than a compound SQL expression element, the operation will still proceed. Additionally, the “adapted” operator will retain its class; previously, a change in class from `InstrumentedAttribute` to `QueryableAttribute` (a superclass) would interact with Python’s operator system such that an expression like `aliased(MyClass.x) > MyClass.x` would reverse itself to read `myclass.x < myclass_1.x`. The adapted attribute will also refer to the new `AliasedClass` as its parent which was not always the case before.

  References: #2872

- [orm] [bug]

  The `viewonly` flag on `relationship()` will now prevent attribute history from being written on behalf of the target attribute. This has the effect of the object not being written to the Session.dirty list if it is mutated. Previously, the object would be present in Session.dirty, but no change would take place on behalf of the modified attribute during flush. The attribute still emits events such as backref events and user-defined events and will still receive mutations from backrefs.

  See also

  viewonly=True on relationship() prevents history from taking effect

  References: #2833

- [orm] [bug]

  Added support for new `Session.info` attribute to `scoped_session`.

- [orm] [bug]

  Fixed bug where usage of new `Bundle` object would cause the `Query.column_descriptions` attribute to fail.

- [orm] [bug] [sql] [sqlite]

  Fixed a regression introduced by the join rewriting feature of #2369 and #2587 where a nested join with one side already an aliased select would fail to translate the ON clause on the outside correctly; in the ORM this could be seen when using a SELECT statement as a “secondary” table.

  References: #2858

### orm declarative

- [orm] [declarative] [bug]

  Declarative does an extra check to detect if the same `Column` is mapped multiple times under different properties (which typically should be a `synonym()` instead) or if two or more `Column` objects are given the same name, raising a warning if this condition is detected.

  References: #2828

- [orm] [declarative] [bug]

  The `DeferredReflection` class has been enhanced to provide automatic reflection support for the “secondary” table referred to by a `relationship()`. “secondary”, when specified either as a string table name, or as a `Table` object with only a name and `MetaData` object will also be included in the reflection process when `DeferredReflection.prepare()` is called.

  References: #2865

- [orm] [declarative] [bug]

  Fixed bug where in Py2K a unicode literal would not be accepted as the string name of a class or other argument within declarative using `relationship()`.

### examples

- [examples] [bug]

  Fixed bug which prevented history_meta recipe from working with joined inheritance schemes more than one level deep.

### engine

- [engine] [feature]

  The `engine_from_config()` function has been improved so that we will be able to parse dialect-specific arguments from string configuration dictionaries. Dialect classes can now provide their own list of parameter types and string-conversion routines. The feature is not yet used by the built-in dialects, however.

  References: #2875

- [engine] [bug]

  A DBAPI that raises an error on `connect()` which is not a subclass of dbapi.Error (such as `TypeError`, `NotImplementedError`, etc.) will propagate the exception unchanged. Previously, the error handling specific to the `connect()` routine would both inappropriately run the exception through the dialect’s `Dialect.is_disconnect()` routine as well as wrap it in a `sqlalchemy.exc.DBAPIError`. It is now propagated unchanged in the same way as occurs within the execute process.

  This change is also backported to: 0.8.4

  References: #2881

- [engine] [bug] [pool]

  The `QueuePool` has been enhanced to not block new connection attempts when an existing connection attempt is blocking. Previously, the production of new connections was serialized within the block that monitored overflow; the overflow counter is now altered within its own critical section outside of the connection process itself.

  This change is also backported to: 0.8.4

  References: #2880

- [engine] [bug] [pool]

  Made a slight adjustment to the logic which waits for a pooled connection to be available, such that for a connection pool with no timeout specified, it will every half a second break out of the wait to check for the so-called “abort” flag, which allows the waiter to break out in case the whole connection pool was dumped; normally the waiter should break out due to a notify_all() but it’s possible this notify_all() is missed in very slim cases. This is an extension of logic first introduced in 0.8.0, and the issue has only been observed occasionally in stress tests.

  This change is also backported to: 0.8.4

  References: #2522

- [engine] [bug]

  Fixed bug where SQL statement would be improperly ASCII-encoded when a pre-DBAPI `StatementError` were raised within `Connection.execute()`, causing encoding errors for non-ASCII statements. The stringification now remains within Python unicode thus avoiding encoding errors.

  This change is also backported to: 0.8.4

  References: #2871

- [engine] [bug]

  The `create_engine()` routine and the related `make_url()` function no longer considers the `+` sign to be a space within the password field. The parsing in this area has been adjusted to match more closely to how RFC 1738 handles these tokens, in that both `username` and `password` expect only `:`, `@`, and `/` to be encoded.

  See also

  The “password” portion of a create_engine() no longer considers the + sign as an encoded space

  References: #2873

- [engine] [bug]

  The `RowProxy` object is now sortable in Python as a regular tuple is; this is accomplished via ensuring tuple() conversion on both sides within the `__eq__()` method as well as the addition of a `__lt__()` method.

  See also

  RowProxy now has tuple-sorting behavior

  References: #2848

### sql

- [sql] [feature]

  New improvements to the `text()` construct, including more flexible ways to set up bound parameters and return types; in particular, a `text()` can now be turned into a full FROM-object, embeddable in other statements as an alias or CTE using the new method `TextClause.columns()`. The `text()` construct can also render “inline” bound parameters when the construct is compiled in a “literal bound” context.

  See also

  New text() Capabilities

  References: #2877, #2882

- [sql] [feature]

  A new API for specifying the `FOR UPDATE` clause of a `SELECT` is added with the new `GenerativeSelect.with_for_update()` method. This method supports a more straightforward system of setting dialect-specific options compared to the `for_update` keyword argument of `select()`, and also includes support for the SQL standard `FOR UPDATE OF` clause. The ORM also includes a new corresponding method `Query.with_for_update()`. Pull request courtesy Mario Lassnig.

  See also

  New FOR UPDATE support on select(), Query()

- [sql] [feature]

  The precision used when coercing a returned floating point value to Python `Decimal` via string is now configurable. The flag `decimal_return_scale` is now supported by all `Numeric` and `Float` types, which will ensure this many digits are taken from the native floating point value when it is converted to string. If not present, the type will make use of the value of `.scale`, if the type supports this setting and it is non-None. Otherwise the original default length of 10 is used.

  See also

  Floating Point String-Conversion Precision Configurable for Native Floating Point Types

  References: #2867

- [sql] [bug]

  Fixed issue where a primary key column that has a Sequence on it, yet the column is not the “auto increment” column, either because it has a foreign key constraint or `autoincrement=False` set, would attempt to fire the Sequence on INSERT for backends that don’t support sequences, when presented with an INSERT missing the primary key value. This would take place on non-sequence backends like SQLite, MySQL.

  This change is also backported to: 0.8.5

  References: #2896

- [sql] [bug]

  Fixed bug with `Insert.from_select()` method where the order of the given names would not be taken into account when generating the INSERT statement, thus producing a mismatch versus the column names in the given SELECT statement. Also noted that `Insert.from_select()` implies that Python-side insert defaults cannot be used, since the statement has no VALUES clause.

  This change is also backported to: 0.8.5

  References: #2895

- [sql] [bug]

  The `cast()` function, when given a plain literal value, will now apply the given type to the given literal value on the bind parameter side according to the type given to the cast, in the same manner as that of the `type_coerce()` function. However unlike `type_coerce()`, this only takes effect if a non-clauseelement value is passed to `cast()`; an existing typed construct will retain its type.

- [sql] [bug]

  The `ForeignKey` class more aggressively checks the given column argument. If not a string, it checks that the object is at least a `ColumnClause`, or an object that resolves to one, and that the `.table` attribute, if present, refers to a `TableClause` or subclass, and not something like an `Alias`. Otherwise, a `ArgumentError` is raised.

  References: #2883

- [sql] [bug]

  The precedence rules for the `ColumnOperators.collate()` operator have been modified, such that the COLLATE operator is now of lower precedence than the comparison operators. This has the effect that a COLLATE applied to a comparison will not render parenthesis around the comparison, which is not parsed by backends such as MSSQL. The change is backwards incompatible for those setups that were working around the issue by applying `Operators.collate()` to an individual element of the comparison expression, rather than the comparison expression as a whole.

  See also

  The precedence rules for COLLATE have been changed

  References: #2879

- [sql] [enhancement]

  The exception raised when a `BindParameter` is present in a compiled statement without a value now includes the key name of the bound parameter in the error message.

  This change is also backported to: 0.8.5

### schema

- [schema] [bug]

  Fixed a regression caused by #2812 where the repr() for table and column names would fail if the name contained non-ascii characters.

  References: #2868

### postgresql

- [postgresql] [feature]

  Support for PostgreSQL JSON has been added, using the new `JSON` type. Huge thanks to Nathan Rice for implementing and testing this.

  References: #2581

- [postgresql] [feature]

  Added support for PostgreSQL TSVECTOR via the `TSVECTOR` type. Pull request courtesy Noufal Ibrahim.

- [postgresql] [bug]

  Fixed bug where index reflection would mis-interpret indkey values when using the pypostgresql adapter, which returns these values as lists vs. psycopg2’s return type of string.

  This change is also backported to: 0.8.4

  References: #2855

- [postgresql] [bug]

  Now using psycopg2 UNICODEARRAY extension for handling unicode arrays with psycopg2 + normal “native unicode” mode, in the same way the UNICODE extension is used.

- [postgresql] [bug]

  Fixed bug where values within an ENUM weren’t escaped for single quote signs. Note that this is backwards-incompatible for existing workarounds that manually escape the single quotes.

  See also

  PostgreSQL CREATE TYPE <x> AS ENUM now applies quoting to values

  References: #2878

### mysql

- [mysql] [bug]

  Improvements to the system by which SQL types generate within `__repr__()`, particularly with regards to the MySQL integer/numeric/ character types which feature a wide variety of keyword arguments. The `__repr__()` is important for use with Alembic autogenerate for when Python code is rendered in a migration script.

  References: #2893

### mssql

- [mssql] [bug] [firebird]

  The “asdecimal” flag used with the `Float` type will now work with Firebird as well as the mssql+pyodbc dialects; previously the decimal conversion was not occurring.

  This change is also backported to: 0.8.5

- [mssql] [bug] [pymssql]

  Added “Net-Lib error during Connection reset by peer” message to the list of messages checked for “disconnect” within the pymssql dialect. Courtesy John Anderson.

  This change is also backported to: 0.8.5

- [mssql] [bug]

  Fixed bug introduced in 0.8.0 where the `DROP INDEX` statement for an index in MSSQL would render incorrectly if the index were in an alternate schema; the schemaname/tablename would be reversed. The format has been also been revised to match current MSSQL documentation. Courtesy Derek Harland.

  This change is also backported to: 0.8.4

### oracle

- [oracle] [bug]

  Added ORA-02396 “maximum idle time” error code to list of “is disconnect” codes with cx_oracle.

  This change is also backported to: 0.8.4

  References: #2864

- [oracle] [bug]

  Fixed bug where Oracle `VARCHAR` types given with no length (e.g. for a `CAST` or similar) would incorrectly render `None CHAR` or similar.

  This change is also backported to: 0.8.4

  References: #2870

### firebird

- [firebird] [bug]

  The firebird dialect will quote identifiers which begin with an underscore. Courtesy Treeve Jelbert.

  This change is also backported to: 0.8.5

  References: #2897

- [firebird] [bug]

  Fixed bug in Firebird index reflection where the columns within the index were not sorted correctly; they are now sorted in order of RDB$FIELD_POSITION.

  This change is also backported to: 0.8.5

- [firebird] [bug]

  Changed the queries used by Firebird to list table and view names to query from the `rdb$relations` view instead of the `rdb$relation_fields` and `rdb$view_relations` views. Variants of both the old and new queries are mentioned on many FAQ and blogs, however the new queries are taken straight from the “Firebird FAQ” which appears to be the most official source of info.

  References: #2898

### misc

- [bug] [declarative]

  Error message when a string arg sent to `relationship()` which doesn’t resolve to a class or mapper has been corrected to work the same way as when a non-string arg is received, which indicates the name of the relationship which had the configurational error.

  This change is also backported to: 0.8.5

  References: #2888

- [bug] [ext]

  Fixed bug which prevented the `serializer` extension from working correctly with table or column names that contain non-ASCII characters.

  This change is also backported to: 0.8.4

  References: #2869

- [removed]

  The “informix” and “informixdb” dialects have been removed; the code is now available as a separate repository on Bitbucket. The IBM-DB project has provided production-level Informix support since the informixdb dialect was first added.

## 0.9.0b1

Released: October 26, 2013

### general

- [general] [feature] [py3k]

  The C extensions are ported to Python 3 and will build under any supported CPython 2 or 3 environment.

  References: #2161

- [general] [feature] [py3k]

  The codebase is now “in-place” for Python 2 and 3, the need to run 2to3 has been removed. Compatibility is now against Python 2.6 on forward.

  References: #2671

- [general]

  A large refactoring of packages has reorganized the import structure of many Core modules as well as some aspects of the ORM modules. In particular `sqlalchemy.sql` has been broken out into several more modules than before so that the very large size of `sqlalchemy.sql.expression` is now pared down. The effort has focused on a large reduction in import cycles. Additionally, the system of API functions in `sqlalchemy.sql.expression` and `sqlalchemy.orm` has been reorganized to eliminate redundancy in documentation between the functions vs. the objects they produce.

### orm

- [orm] [feature]

  Added new option to `relationship()` `distinct_target_key`. This enables the subquery eager loader strategy to apply a DISTINCT to the innermost SELECT subquery, to assist in the case where duplicate rows are generated by the innermost query which corresponds to this relationship (there’s not yet a general solution to the issue of dupe rows within subquery eager loading, however, when joins outside of the innermost subquery produce dupes). When the flag is set to `True`, the DISTINCT is rendered unconditionally, and when it is set to `None`, DISTINCT is rendered if the innermost relationship targets columns that do not comprise a full primary key. The option defaults to False in 0.8 (e.g. off by default in all cases), None in 0.9 (e.g. automatic by default). Thanks to Alexander Koval for help with this.

  See also

  Subquery Eager Loading will apply DISTINCT to the innermost SELECT for some queries

  This change is also backported to: 0.8.3

  References: #2836

- [orm] [feature]

  The association proxy now returns `None` when fetching a scalar attribute off of a scalar relationship, where the scalar relationship itself points to `None`, instead of raising an `AttributeError`.

  See also

  Association Proxy Missing Scalar returns None

  References: #2810

- [orm] [feature]

  Added new method `AttributeState.load_history()`, works like `AttributeState.history` but also fires loader callables.

  See also

  attributes.get_history() will query from the DB by default if value not present

  References: #2787

- [orm] [feature]

  Added a new load option `load_only()`. This allows a series of column names to be specified as loading “only” those attributes, deferring the rest.

  References: #1418

- [orm] [feature]

  The system of loader options has been entirely rearchitected to build upon a much more comprehensive base, the `Load` object. This base allows any common loader option like `joinedload()`, `defer()`, etc. to be used in a “chained” style for the purpose of specifying options down a path, such as `joinedload("foo").subqueryload("bar")`. The new system supersedes the usage of dot-separated path names, multiple attributes within options, and the usage of `_all()` options.

  See also

  New Query Options API; load_only() option

  References: #1418

- [orm] [feature]

  The `composite()` construct now maintains the return object when used in a column-oriented `Query`, rather than expanding out into individual columns. This makes use of the new `Bundle` feature internally. This behavior is backwards incompatible; to select from a composite column which will expand out, use `MyClass.some_composite.clauses`.

  See also

  Composite attributes are now returned as their object form when queried on a per-attribute basis

  References: #2824

- [orm] [feature]

  A new construct `Bundle` is added, which allows for specification of groups of column expressions to a `Query` construct. The group of columns are returned as a single tuple by default. The behavior of `Bundle` can be overridden however to provide any sort of result processing to the returned row. The behavior of `Bundle` is also embedded into composite attributes now when they are used in a column-oriented `Query`.

  See also

  Column Bundles for ORM queries

  Composite attributes are now returned as their object form when queried on a per-attribute basis

  References: #2824

- [orm] [feature]

  The `version_id_generator` parameter of `Mapper` can now be specified to rely upon server generated version identifiers, using triggers or other database-provided versioning features, or via an optional programmatic value, by setting `version_id_generator=False`. When using a server-generated version identifier, the ORM will use RETURNING when available to immediately load the new version value, else it will emit a second SELECT.

  References: #2793

- [orm] [feature]

  The `eager_defaults` flag of `Mapper` will now allow the newly generated default values to be fetched using an inline RETURNING clause, rather than a second SELECT statement, for backends that support RETURNING.

  References: #2793

- [orm] [feature]

  Added a new attribute `Session.info` to `Session`; this is a dictionary where applications can store arbitrary data local to a `Session`. The contents of `Session.info` can be also be initialized using the `info` argument of `Session` or `sessionmaker`.

- [orm] [feature]

  Removal of event listeners is now implemented. The feature is provided via the `remove()` function.

  See also

  Event Removal API

  References: #2268

- [orm] [feature]

  The mechanism by which attribute events pass along an `AttributeImpl` as an “initiator” token has been changed; the object is now an event-specific object called `Event`. Additionally, the attribute system no longer halts events based on a matching “initiator” token; this logic has been moved to be specific to ORM backref event handlers, which are the typical source of the re-propagation of an attribute event onto subsequent append/set/remove operations. End user code which emulates the behavior of backrefs must now ensure that recursive event propagation schemes are halted, if the scheme does not use the backref handlers. Using this new system, backref handlers can now perform a “two-hop” operation when an object is appended to a collection, associated with a new many-to-one, de-associated with the previous many-to-one, and then removed from a previous collection. Before this change, the last step of removal from the previous collection would not occur.

  See also

  Backref handlers can now propagate more than one level deep

  References: #2789

- [orm] [feature]

  A major change regarding how the ORM constructs joins where the right side is itself a join or left outer join. The ORM is now configured to allow simple nesting of joins of the form `a JOIN (b JOIN c ON b.id=c.id) ON a.id=b.id`, rather than forcing the right side into a `SELECT` subquery. This should allow significant performance improvements on most backends, most particularly MySQL. The one database backend that has for many years held back this change, SQLite, is now addressed by moving the production of the `SELECT` subquery from the ORM to the SQL compiler; so that a right-nested join on SQLite will still ultimately render with a `SELECT`, while all other backends are no longer impacted by this workaround.

  As part of this change, a new argument `flat=True` has been added to the `aliased()`, `Join.alias()`, and `with_polymorphic()` functions, which allows an “alias” of a JOIN to be produced which applies an anonymous alias to each component table within the join, rather than producing a subquery.

  See also

  Many JOIN and LEFT OUTER JOIN expressions will no longer be wrapped in (SELECT * FROM ..) AS ANON_1

  References: #2587

- [orm] [bug]

  Fixed bug where using an annotation such as `remote()` or `foreign()` on a `Column` before association with a parent `Table` could produce issues related to the parent table not rendering within joins, due to the inherent copy operation performed by an annotation.

  This change is also backported to: 0.8.3

  References: #2813

- [orm] [bug]

  Fixed bug where `Query.exists()` failed to work correctly without any WHERE criterion. Courtesy Vladimir Magamedov.

  This change is also backported to: 0.8.3

  References: #2818

- [orm] [bug]

  Fixed a potential issue in an ordered sequence implementation used by the ORM to iterate mapper hierarchies; under the Jython interpreter this implementation wasn’t ordered, even though cPython and PyPy maintained ordering.

  This change is also backported to: 0.8.3

  References: #2794

- [orm] [bug]

  Fixed bug in ORM-level event registration where the “raw” or “propagate” flags could potentially be mis-configured in some “unmapped base class” configurations.

  This change is also backported to: 0.8.3

  References: #2786

- [orm] [bug]

  A performance fix related to the usage of the `defer()` option when loading mapped entities. The function overhead of applying a per-object deferred callable to an instance at load time was significantly higher than that of just loading the data from the row (note that `defer()` is meant to reduce DB/network overhead, not necessarily function call count); the function call overhead is now less than that of loading data from the column in all cases. There is also a reduction in the number of “lazy callable” objects created per load from N (total deferred values in the result) to 1 (total number of deferred cols).

  This change is also backported to: 0.8.3

  References: #2778

- [orm] [bug]

  Fixed bug whereby attribute history functions would fail when an object we moved from “persistent” to “pending” using the `make_transient()` function, for operations involving collection-based backrefs.

  This change is also backported to: 0.8.3

  References: #2773

- [orm] [bug]

  A warning is emitted when trying to flush an object of an inherited class where the polymorphic discriminator has been assigned to a value that is invalid for the class.

  This change is also backported to: 0.8.2

  References: #2750

- [orm] [bug]

  Fixed bug in polymorphic SQL generation where multiple joined-inheritance entities against the same base class joined to each other as well would not track columns on the base table independently of each other if the string of joins were more than two entities long.

  This change is also backported to: 0.8.2

  References: #2759

- [orm] [bug]

  Fixed bug where sending a composite attribute into `Query.order_by()` would produce a parenthesized expression not accepted by some databases.

  This change is also backported to: 0.8.2

  References: #2754

- [orm] [bug]

  Fixed the interaction between composite attributes and the `aliased()` function. Previously, composite attributes wouldn’t work correctly in comparison operations when aliasing was applied.

  This change is also backported to: 0.8.2

  References: #2755

- [orm] [bug] [ext]

  Fixed bug where `MutableDict` didn’t report a change event when `clear()` was called.

  This change is also backported to: 0.8.2

  References: #2730

- [orm] [bug]

  Fixed bug where list instrumentation would fail to represent a setslice of `[0:0]` correctly, which in particular could occur when using `insert(0, item)` with the association proxy. Due to some quirk in Python collections, the issue was much more likely with Python 3 rather than 2.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2807

- [orm] [bug]

  `get_history()` when used with a scalar column-mapped attribute will now honor the “passive” flag passed to it; as this defaults to `PASSIVE_OFF`, the function will by default query the database if the value is not present. This is a behavioral change vs. 0.8.

  See also

  attributes.get_history() will query from the DB by default if value not present

  References: #2787

- [orm] [bug] [associationproxy]

  Added additional criterion to the ==, != comparators, used with scalar values, for comparisons to None to also take into account the association record itself being non-present, in addition to the existing test for the scalar endpoint on the association record being NULL. Previously, comparing `Cls.scalar == None` would return records for which `Cls.associated` were present and `Cls.associated.scalar` is None, but not rows for which `Cls.associated` is non-present. More significantly, the inverse operation `Cls.scalar != None` would return `Cls` rows for which `Cls.associated` was non-present.

  The case for `Cls.scalar != 'somevalue'` is also modified to act more like a direct SQL comparison; only rows for which `Cls.associated` is present and `Associated.scalar` is non-NULL and not equal to `'somevalue'` are returned. Previously, this would be a simple `NOT EXISTS`.

  Also added a special use case where you can call `Cls.scalar.has()` with no arguments, when `Cls.scalar` is a column-based value - this returns whether or not `Cls.associated` has any rows present, regardless of whether or not `Cls.associated.scalar` is NULL or not.

  See also

  Association Proxy SQL Expression Improvements and Fixes

  References: #2751

- [orm] [bug]

  Fixed an obscure bug where the wrong results would be fetched when joining/joinedloading across a many-to-many relationship to a single-table-inheriting subclass with a specific discriminator value, due to “secondary” rows that would come back. The “secondary” and right-side tables are now inner joined inside of parenthesis for all ORM joins on many-to-many relationships so that the left->right join can accurately filtered. This change was made possible by finally addressing the issue with right-nested joins outlined in #2587.

  See also

  Many JOIN and LEFT OUTER JOIN expressions will no longer be wrapped in (SELECT * FROM ..) AS ANON_1

  References: #2369

- [orm] [bug]

  The “auto-aliasing” behavior of the `Query.select_from()` method has been turned off. The specific behavior is now available via a new method `Query.select_entity_from()`. The auto-aliasing behavior here was never well documented and is generally not what’s desired, as `Query.select_from()` has become more oriented towards controlling how a JOIN is rendered. `Query.select_entity_from()` will also be made available in 0.8 so that applications which rely on the auto-aliasing can shift their applications to use this method.

  See also

  _query.Query.select_from() no longer applies the clause to corresponding entities

  References: #2736

### orm declarative

- [orm] [declarative] [feature]

  Added a convenience class decorator `as_declarative()`, is a wrapper for `declarative_base()` which allows an existing base class to be applied using a nifty class-decorated approach.

  This change is also backported to: 0.8.3

- [orm] [declarative] [feature]

  ORM descriptors such as hybrid properties can now be referenced by name in a string argument used with `order_by`, `primaryjoin`, or similar in `relationship()`, in addition to column-bound attributes.

  This change is also backported to: 0.8.2

  References: #2761

### examples

- [examples] [feature]

  Improved the examples in `examples/generic_associations`, including that `discriminator_on_association.py` makes use of single table inheritance do the work with the “discriminator”. Also added a true “generic foreign key” example, which works similarly to other popular frameworks in that it uses an open-ended integer to point to any other table, foregoing traditional referential integrity. While we don’t recommend this pattern, information wants to be free.

  This change is also backported to: 0.8.3

- [examples] [bug]

  Added “autoincrement=False” to the history table created in the versioning example, as this table shouldn’t have autoinc on it in any case, courtesy Patrick Schmid.

  This change is also backported to: 0.8.3

- [examples] [bug]

  Fixed an issue with the “versioning” recipe whereby a many-to-one reference could produce a meaningless version for the target, even though it was not changed, when backrefs were present. Patch courtesy Matt Chisholm.

  This change is also backported to: 0.8.2

### engine

- [engine] [feature]

  `repr()` for the `URL` of an `Engine` will now conceal the password using asterisks. Courtesy Gunnlaugur Þór Briem.

  This change is also backported to: 0.8.3

  References: #2821

- [engine] [feature]

  New events added to `ConnectionEvents`:

  - `ConnectionEvents.engine_connect()`

  - `ConnectionEvents.set_connection_execution_options()`

  - `ConnectionEvents.set_engine_execution_options()`

  References: #2770

- [engine] [bug] [oracle]

  Dialect.initialize() is not called a second time if an `Engine` is recreated, due to a disconnect error. This fixes a particular issue in the Oracle 8 dialect, but in general the dialect.initialize() phase should only be once per dialect.

  This change is also backported to: 0.8.3

  References: #2776

- [engine] [bug] [pool]

  Fixed bug where `QueuePool` would lose the correct checked out count if an existing pooled connection failed to reconnect after an invalidate or recycle event.

  This change is also backported to: 0.8.3

  References: #2772

- [engine] [bug]

  Fixed bug where the `reset_on_return` argument to various `Pool` implementations would not be propagated when the pool was regenerated. Courtesy Eevee.

  This change is also backported to: 0.8.2

- [engine] [bug]

  The regexp used by the `make_url()` function now parses ipv6 addresses, e.g. surrounded by brackets.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2851

- [engine] [bug]

  The method signature of `Dialect.reflecttable()`, which in all known cases is provided by `DefaultDialect`, has been tightened to expect `include_columns` and `exclude_columns` arguments without any kw option, reducing ambiguity - previously `exclude_columns` was missing.

  References: #2748

### sql

- [sql] [feature]

  Added support for “unique constraint” reflection, via the `Inspector.get_unique_constraints()` method. Thanks for Roman Podolyaka for the patch.

  This change is also backported to: 0.8.4

  References: #1443

- [sql] [feature]

  The `update()`, `insert()`, and `delete()` constructs will now interpret ORM entities as target tables to be operated upon, e.g.:

      from sqlalchemy import insert, update, delete

      ins = insert(SomeMappedClass).values(x=5)

      del_ = delete(SomeMappedClass).where(SomeMappedClass.id == 5)

      upd = update(SomeMappedClass).where(SomeMappedClass.id == 5).values(name="ed")

  This change is also backported to: 0.8.3

- [sql] [feature] [mysql] [postgresql]

  The PostgreSQL and MySQL dialects now support reflection/inspection of foreign key options, including ON UPDATE, ON DELETE. PostgreSQL also reflects MATCH, DEFERRABLE, and INITIALLY. Courtesy ijl.

  References: #2183

- [sql] [feature]

  A `bindparam()` construct with a “null” type (e.g. no type specified) is now copied when used in a typed expression, and the new copy is assigned the actual type of the compared column. Previously, this logic would occur on the given `bindparam()` in place. Additionally, a similar process now occurs for `bindparam()` constructs passed to `ValuesBase.values()` for an `Insert` or `Update` construct, within the compilation phase of the construct.

  These are both subtle behavioral changes which may impact some usages.

  See also

  A bindparam() construct with no type gets upgraded via copy when a type is available

  References: #2850

- [sql] [feature]

  An overhaul of expression handling for special symbols particularly with conjunctions, e.g. `None` `null()` `true()` `false()`, including consistency in rendering NULL in conjunctions, “short-circuiting” of `and_()` and `or_()` expressions which contain boolean constants, and rendering of boolean constants and expressions as compared to “1” or “0” for backends that don’t feature `true`/`false` constants.

  See also

  Improved rendering of Boolean constants, NULL constants, conjunctions

  References: #2734, #2804, #2823

- [sql] [feature]

  The typing system now handles the task of rendering “literal bind” values, e.g. values that are normally bound parameters but due to context must be rendered as strings, typically within DDL constructs such as CHECK constraints and indexes (note that “literal bind” values become used by DDL as of #2742). A new method `TypeEngine.literal_processor()` serves as the base, and `TypeDecorator.process_literal_param()` is added to allow wrapping of a native literal rendering method.

  See also

  The typing system now handles the task of rendering “literal bind” values

  References: #2838

- [sql] [feature]

  The `Table.tometadata()` method now produces copies of all `SchemaItem.info` dictionaries from all `SchemaItem` objects within the structure including columns, constraints, foreign keys, etc. As these dictionaries are copies, they are independent of the original dictionary. Previously, only the `.info` dictionary of `Column` was transferred within this operation, and it was only linked in place, not copied.

  References: #2716

- [sql] [feature]

  The `default` argument of `Column` now accepts a class or object method as an argument, in addition to a standalone function; will properly detect if the “context” argument is accepted or not.

- [sql] [feature]

  Added new method to the `insert()` construct `Insert.from_select()`. Given a list of columns and a selectable, renders `INSERT INTO (table) (columns) SELECT ..`. While this feature is highlighted as part of 0.9 it is also backported to 0.8.3.

  See also

  INSERT from SELECT

  References: #722

- [sql] [feature]

  Provided a new attribute for `TypeDecorator` called `TypeDecorator.coerce_to_is_types`, to make it easier to control how comparisons using `==` or `!=` to `None` and boolean types goes about producing an `IS` expression, or a plain equality expression with a bound parameter.

  References: #2734, #2744

- [sql] [feature]

  A `label()` construct will now render as its name alone in an `ORDER BY` clause, if that label is also referred to in the columns clause of the select, instead of rewriting the full expression. This gives the database a better chance to optimize the evaluation of the same expression in two different contexts.

  See also

  Label constructs can now render as their name alone in an ORDER BY

  References: #1068

- [sql] [bug]

  Fixed bug where `type_coerce()` would not interpret ORM elements with a `__clause_element__()` method properly.

  This change is also backported to: 0.8.3

  References: #2849

- [sql] [bug]

  The `Enum` and `Boolean` types now bypass any custom (e.g. TypeDecorator) type in use when producing the CHECK constraint for the “non native” type. This so that the custom type isn’t involved in the expression within the CHECK, since this expression is against the “impl” value and not the “decorated” value.

  This change is also backported to: 0.8.3

  References: #2842

- [sql] [bug]

  The `.unique` flag on `Index` could be produced as `None` if it was generated from a `Column` that didn’t specify `unique` (where it defaults to `None`). The flag will now always be `True` or `False`.

  This change is also backported to: 0.8.3

  References: #2825

- [sql] [bug]

  Fixed bug in default compiler plus those of postgresql, mysql, and mssql to ensure that any literal SQL expression values are rendered directly as literals, instead of as bound parameters, within a CREATE INDEX statement. This also changes the rendering scheme for other DDL such as constraints.

  This change is also backported to: 0.8.3

  References: #2742

- [sql] [bug]

  A `select()` that is made to refer to itself in its FROM clause, typically via in-place mutation, will raise an informative error message rather than causing a recursion overflow.

  This change is also backported to: 0.8.3

  References: #2815

- [sql] [bug]

  Fixed bug where using the `column_reflect` event to change the `.key` of the incoming `Column` would prevent primary key constraints, indexes, and foreign key constraints from being correctly reflected.

  This change is also backported to: 0.8.3

  References: #2811

- [sql] [bug]

  The `ColumnOperators.notin_()` operator added in 0.8 now properly produces the negation of the expression “IN” returns when used against an empty collection.

  This change is also backported to: 0.8.3

- [sql] [bug] [postgresql]

  Fixed bug where the expression system relied upon the `str()` form of a some expressions when referring to the `.c` collection on a `select()` construct, but the `str()` form isn’t available since the element relies on dialect-specific compilation constructs, notably the `__getitem__()` operator as used with a PostgreSQL `ARRAY` element. The fix also adds a new exception class `UnsupportedCompilationError` which is raised in those cases where a compiler is asked to compile something it doesn’t know how to.

  This change is also backported to: 0.8.3

  References: #2780

- [sql] [bug]

  Multiple fixes to the correlation behavior of `Select` constructs, first introduced in 0.8.0:

  - To satisfy the use case where FROM entries should be correlated outwards to a SELECT that encloses another, which then encloses this one, correlation now works across multiple levels when explicit correlation is established via `Select.correlate()`, provided that the target select is somewhere along the chain contained by a WHERE/ORDER BY/columns clause, not just nested FROM clauses. This makes `Select.correlate()` act more compatibly to that of 0.7 again while still maintaining the new “smart” correlation.

  - When explicit correlation is not used, the usual “implicit” correlation limits its behavior to just the immediate enclosing SELECT, to maximize compatibility with 0.7 applications, and also prevents correlation across nested FROMs in this case, maintaining compatibility with 0.8.0/0.8.1.

  - The `Select.correlate_except()` method was not preventing the given FROM clauses from correlation in all cases, and also would cause FROM clauses to be incorrectly omitted entirely (more like what 0.7 would do), this has been fixed.

  - Calling select.correlate_except(None) will enter all FROM clauses into correlation as would be expected.

  This change is also backported to: 0.8.2

  References: #2668, #2746

- [sql] [bug]

  Fixed bug whereby joining a select() of a table “A” with multiple foreign key paths to a table “B”, to that table “B”, would fail to produce the “ambiguous join condition” error that would be reported if you join table “A” directly to “B”; it would instead produce a join condition with multiple criteria.

  This change is also backported to: 0.8.2

  References: #2738

- [sql] [bug] [reflection]

  Fixed bug whereby using `MetaData.reflect()` across a remote schema as well as a local schema could produce wrong results in the case where both schemas had a table of the same name.

  This change is also backported to: 0.8.2

  References: #2728

- [sql] [bug]

  Removed the “not implemented” `__iter__()` call from the base `ColumnOperators` class, while this was introduced in 0.8.0 to prevent an endless, memory-growing loop when one also implements a `__getitem__()` method on a custom operator and then calls erroneously `list()` on that object, it had the effect of causing column elements to report that they were in fact iterable types which then throw an error when you try to iterate. There’s no real way to have both sides here so we stick with Python best practices. Careful with implementing `__getitem__()` on your custom operators!

  This change is also backported to: 0.8.2

  References: #2726

- [sql] [bug]

  Fixed regression dating back to 0.7.9 whereby the name of a CTE might not be properly quoted if it was referred to in multiple FROM clauses.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2801

- [sql] [bug] [cte]

  Fixed bug in common table expression system where if the CTE were used only as an `alias()` construct, it would not render using the WITH keyword.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2783

- [sql] [bug]

  Fixed bug in `CheckConstraint` DDL where the “quote” flag from a `Column` object would not be propagated.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2784

- [sql] [bug]

  The “name” attribute is set on `Index` before the “attach” events are called, so that attachment events can be used to dynamically generate a name for the index based on the parent table and/or columns.

  References: #2835

- [sql] [bug]

  The erroneous kw arg “schema” has been removed from the `ForeignKey` object. this was an accidental commit that did nothing; a warning is raised in 0.8.3 when this kw arg is used.

  References: #2831

- [sql] [bug]

  A rework to the way that “quoted” identifiers are handled, in that instead of relying upon various `quote=True` flags being passed around, these flags are converted into rich string objects with quoting information included at the point at which they are passed to common schema constructs like `Table`, `Column`, etc. This solves the issue of various methods that don’t correctly honor the “quote” flag such as `Engine.has_table()` and related methods. The `quoted_name` object is a string subclass that can also be used explicitly if needed; the object will hold onto the quoting preferences passed and will also bypass the “name normalization” performed by dialects that standardize on uppercase symbols, such as Oracle, Firebird and DB2. The upshot is that the “uppercase” backends can now work with force-quoted names, such as lowercase-quoted names and new reserved words.

  See also

  Schema identifiers now carry along their own quoting information

  References: #2812

- [sql] [bug]

  The resolution of `ForeignKey` objects to their target `Column` has been reworked to be as immediate as possible, based on the moment that the target `Column` is associated with the same `MetaData` as this `ForeignKey`, rather than waiting for the first time a join is constructed, or similar. This along with other improvements allows earlier detection of some foreign key configuration issues. Also included here is a rework of the type-propagation system, so that it should be reliable now to set the type as `None` on any `Column` that refers to another via `ForeignKey` - the type will be copied from the target column as soon as that other column is associated, and now works for composite foreign keys as well.

  See also

  Columns can reliably get their type from a column referred to via ForeignKey

  References: #1765

### postgresql

- [postgresql] [feature]

  Support for PostgreSQL 9.2 range types has been added. Currently, no type translation is provided, so works directly with strings or psycopg2 2.5 range extension types at the moment. Patch courtesy Chris Withers.

  This change is also backported to: 0.8.2

- [postgresql] [feature]

  Added support for “AUTOCOMMIT” isolation when using the psycopg2 DBAPI. The keyword is available via the `isolation_level` execution option. Patch courtesy Roman Podolyaka.

  This change is also backported to: 0.8.2

  References: #2072

- [postgresql] [feature]

  Added support for rendering `SMALLSERIAL` when a `SmallInteger` type is used on a primary key autoincrement column, based on server version detection of PostgreSQL version 9.2 or greater.

  References: #2840

- [postgresql] [bug]

  Removed a 128-character truncation from the reflection of the server default for a column; this code was original from PG system views which truncated the string for readability.

  This change is also backported to: 0.8.3

  References: #2844

- [postgresql] [bug]

  Parenthesis will be applied to a compound SQL expression as rendered in the column list of a CREATE INDEX statement.

  This change is also backported to: 0.8.3

  References: #2742

- [postgresql] [bug]

  Fixed bug where PostgreSQL version strings that had a prefix preceding the words “PostgreSQL” or “EnterpriseDB” would not parse. Courtesy Scott Schaefer.

  This change is also backported to: 0.8.3

  References: #2819

- [postgresql] [bug]

  The behavior of `extract()` has been simplified on the PostgreSQL dialect to no longer inject a hardcoded `::timestamp` or similar cast into the given expression, as this interfered with types such as timezone-aware datetimes, but also does not appear to be at all necessary with modern versions of psycopg2.

  This change is also backported to: 0.8.2

  References: #2740

- [postgresql] [bug]

  Fixed bug in HSTORE type where keys/values that contained backslashed quotes would not be escaped correctly when using the “non native” (i.e. non-psycopg2) means of translating HSTORE data. Patch courtesy Ryan Kelly.

  This change is also backported to: 0.8.2

  References: #2766

- [postgresql] [bug]

  Fixed bug where the order of columns in a multi-column PostgreSQL index would be reflected in the wrong order. Courtesy Roman Podolyaka.

  This change is also backported to: 0.8.2

  References: #2767

### mysql

- [mysql] [feature]

  The `mysql_length` parameter used with `Index` can now be passed as a dictionary of column names/lengths, for use with composite indexes. Big thanks to Roman Podolyaka for the patch.

  This change is also backported to: 0.8.2

  References: #2704

- [mysql] [feature]

  The MySQL `SET` type now features the same auto-quoting behavior as that of `ENUM`. Quotes are not required when setting up the value, but quotes that are present will be auto-detected along with a warning. This also helps with Alembic where the SET type doesn’t render with quotes.

  References: #2817

- [mysql] [bug]

  The change in #2721, which is that the `deferrable` keyword of `ForeignKeyConstraint` is silently ignored on the MySQL backend, will be reverted as of 0.9; this keyword will now render again, raising errors on MySQL as it is not understood - the same behavior will also apply to the `initially` keyword. In 0.8, the keywords will remain ignored but a warning is emitted. Additionally, the `match` keyword now raises a `CompileError` on 0.9 and emits a warning on 0.8; this keyword is not only silently ignored by MySQL but also breaks the ON UPDATE/ON DELETE options.

  To use a `ForeignKeyConstraint` that does not render or renders differently on MySQL, use a custom compilation option. An example of this usage has been added to the documentation, see MySQL / MariaDB Foreign Keys.

  This change is also backported to: 0.8.3

  References: #2721, #2839

- [mysql] [bug]

  MySQL-connector dialect now allows options in the create_engine query string to override those defaults set up in the connect, including “buffered” and “raise_on_warnings”.

  This change is also backported to: 0.8.3

  References: #2515

- [mysql] [bug]

  Fixed bug when using multi-table UPDATE where a supplemental table is a SELECT with its own bound parameters, where the positioning of the bound parameters would be reversed versus the statement itself when using MySQL’s special syntax.

  This change is also backported to: 0.8.2

  References: #2768

- [mysql] [bug]

  Added another conditional to the `mysql+gaerdbms` dialect to detect so-called “development” mode, where we should use the `rdbms_mysqldb` DBAPI. Patch courtesy Brett Slatkin.

  This change is also backported to: 0.8.2

  References: #2715

- [mysql] [bug]

  The `deferrable` keyword argument on `ForeignKey` and `ForeignKeyConstraint` will not render the `DEFERRABLE` keyword on the MySQL dialect. For a long time we left this in place because a non-deferrable foreign key would act very differently than a deferrable one, but some environments just disable FKs on MySQL, so we’ll be less opinionated here.

  This change is also backported to: 0.8.2

  References: #2721

- [mysql] [bug]

  Updates to MySQL reserved words for versions 5.5, 5.6, courtesy Hanno Schlichting.

  This change is also backported to: 0.8.3, 0.8.0b1

  References: #2791

- [mysql] [bug]

  Fix and test parsing of MySQL foreign key options within reflection; this complements the work in #2183 where we begin to support reflection of foreign key options such as ON UPDATE/ON DELETE cascade.

  References: #2839

- [mysql] [bug]

  Improved support for the cymysql driver, supporting version 0.6.5, courtesy Hajime Nakagami.

### sqlite

- [sqlite] [bug]

  The newly added SQLite DATETIME arguments storage_format and regexp apparently were not fully implemented correctly; while the arguments were accepted, in practice they would have no effect; this has been fixed.

  This change is also backported to: 0.8.3

  References: #2781

- [sqlite] [bug]

  Added `sqlalchemy.types.BIGINT` to the list of type names that can be reflected by the SQLite dialect; courtesy Russell Stuart.

  This change is also backported to: 0.8.2

  References: #2764

### mssql

- [mssql] [bug]

  When querying the information schema on SQL Server 2000, removed a CAST call that was added in 0.8.1 to help with driver issues, which apparently is not compatible on 2000. The CAST remains in place for SQL Server 2005 and greater.

  This change is also backported to: 0.8.2

  References: #2747

- [mssql] [bug] [pyodbc]

  Fixes to MSSQL with Python 3 + pyodbc, including that statements are passed correctly.

  References: #2355

### oracle

- [oracle] [feature] [py3k]

  The Oracle unit tests with cx_oracle now pass fully under Python 3.

- [oracle] [bug]

  Fixed bug where Oracle table reflection using synonyms would fail if the synonym and the table were in different remote schemas. Patch to fix courtesy Kyle Derr.

  This change is also backported to: 0.8.3

  References: #2853

### firebird

- [firebird] [feature]

  Added new flag `retaining=True` to the kinterbasdb and fdb dialects. This controls the value of the `retaining` flag sent to the `commit()` and `rollback()` methods of the DBAPI connection. Due to historical concerns, this flag defaults to `True` in 0.8.2, however in 0.9.0b1 this flag defaults to `False`.

  This change is also backported to: 0.8.2

  References: #2763

- [firebird] [feature]

  The `fdb` dialect is now the default dialect when specified without a dialect qualifier, i.e. `firebird://`, per the Firebird project publishing `fdb` as their official Python driver.

  References: #2504

- [firebird] [bug]

  Type lookup when reflecting the Firebird types LONG and INT64 has been fixed so that LONG is treated as INTEGER, INT64 treated as BIGINT, unless the type has a “precision” in which case it’s treated as NUMERIC. Patch courtesy Russell Stuart.

  This change is also backported to: 0.8.2

  References: #2757

### misc

- [feature]

  Added a new flag `system=True` to `Column`, which marks the column as a “system” column which is automatically made present by the database (such as PostgreSQL `oid` or `xmin`). The column will be omitted from the `CREATE TABLE` statement but will otherwise be available for querying. In addition, the `CreateColumn` construct can be applied to a custom compilation rule which allows skipping of columns, by producing a rule that returns `None`.

  This change is also backported to: 0.8.3

- [feature] [core]

  Added a new variant to `UpdateBase.returning()` called `ValuesBase.return_defaults()`; this allows arbitrary columns to be added to the RETURNING clause of the statement without interfering with the compilers usual “implicit returning” feature, which is used to efficiently fetch newly generated primary key values. For supporting backends, a dictionary of all fetched values is present at `ResultProxy.returned_defaults`.

  References: #2793

- [feature] [pool]

  Added pool logging for “rollback-on-return” and the less used “commit-on-return”. This is enabled with the rest of pool “debug” logging.

  References: #2752

- [bug] [ext]

  Fixed bug whereby if a composite type were set up with a function instead of a class, the mutable extension would trip up when it tried to check that column for being a `MutableComposite` (which it isn’t). Courtesy asldevi.

  This change is also backported to: 0.8.2

- [requirements]

  The Python mock library is now required in order to run the unit test suite. While part of the standard library as of Python 3.3, previous Python installations will need to install this in order to run unit tests or to use the `sqlalchemy.testing` package for external dialects.

  This change is also backported to: 0.8.2