Release: 1.4.44 | Release Date: November 12, 2022

# SQLAlchemy 1.4 Documentation

# The Type Hierarchy

SQLAlchemy provides abstractions for most common database data types, as well as several techniques for customization of datatypes.

Database types are represented using Python classes, all of which ultimately extend from the base type class known as `TypeEngine`. There are two general categories of datatypes, each of which express themselves within the typing hierarchy in different ways. The category used by an individual datatype class can be identified based on the use of two different naming conventions, which are “CamelCase” and “UPPERCASE”.

See also

Setting up MetaData with Table objects - in the SQLAlchemy 1.4 / 2.0 Tutorial. Illustrates the most rudimental use of `TypeEngine` type objects to define `Table` metadata and introduces the concept of type objects in tutorial form.

## The “CamelCase” datatypes

The rudimental types have “CamelCase” names such as `String`, `Numeric`, `Integer`, and `DateTime`. All of the immediate subclasses of `TypeEngine` are “CamelCase” types. The “CamelCase” types are to the greatest degree possible database agnostic, meaning they can all be used on any database backend where they will behave in such a way as appropriate to that backend in order to produce the desired behavior.

An example of a straightforward “CamelCase” datatype is `String`. On most backends, using this datatype in a table specification will correspond to the `VARCHAR` database type being used on the target backend, delivering string values to and from the database, as in the example below:

    from sqlalchemy import MetaData
    from sqlalchemy import Table, Column, Integer, String

    metadata_obj = MetaData()

    user = Table(
        "user",
        metadata_obj,
        Column("user_name", String, primary_key=True),
        Column("email_address", String(60)),
    )

When using a particular `TypeEngine` class in a `Table` definition or in any SQL expression overall, if no arguments are required it may be passed as the class itself, that is, without instantiating it with `()`. If arguments are needed, such as the length argument of 60 in the `"email_address"` column above, the type may be instantiated.

Another “CamelCase” datatype that expresses more backend-specific behavior is the `Boolean` datatype. Unlike `String`, which represents a string datatype that all databases have, not every backend has a real “boolean” datatype; some make use of integers or BIT values 0 and 1, some have boolean literal constants `true` and `false` while others dont. For this datatype, `Boolean` may render `BOOLEAN` on a backend such as PostgreSQL, `BIT` on the MySQL backend and `SMALLINT` on Oracle. As data is sent and received from the database using this type, based on the dialect in use it may be interpreting Python numeric or boolean values.

The typical SQLAlchemy application will likely wish to use primarily “CamelCase” types in the general case, as they will generally provide the best basic behavior and be automatically portable to all backends.

Reference for the general set of “CamelCase” datatypes is below at Generic “CamelCase” Types.

## The “UPPERCASE” datatypes

In contrast to the “CamelCase” types are the “UPPERCASE” datatypes. These datatypes are always inherited from a particular “CamelCase” datatype, and always represent an exact datatype. When using an “UPPERCASE” datatype, the name of the type is always rendered exactly as given, without regard for whether or not the current backend supports it. Therefore the use of “UPPERCASE” types in a SQLAlchemy application indicates that specific datatypes are required, which then implies that the application would normally, without additional steps taken, be limited to those backends which use the type exactly as given. Examples of UPPERCASE types include `VARCHAR`, `NUMERIC`, `INTEGER`, and `TIMESTAMP`, which inherit directly from the previously mentioned “CamelCase” types `String`, `Numeric`, `Integer`, and `DateTime`, respectively.

The “UPPERCASE” datatypes that are part of `sqlalchemy.types` are common SQL types that typically expect to be available on at least two backends if not more.

Reference for the general set of “UPPERCASE” datatypes is below at SQL Standard and Multiple Vendor “UPPERCASE” Types.

## Backend-specific “UPPERCASE” datatypes

Most databases also have their own datatypes that are either fully specific to those databases, or add additional arguments that are specific to those databases. For these datatypes, specific SQLAlchemy dialects provide backend-specific “UPPERCASE” datatypes, for a SQL type that has no analogue on other backends. Examples of backend-specific uppercase datatypes include PostgreSQL’s `JSONB`, SQL Server’s `IMAGE` and MySQL’s `TINYTEXT`.

Specific backends may also include “UPPERCASE” datatypes that extend the arguments available from that same “UPPERCASE” datatype as found in the `sqlalchemy.types` module. An example is when creating a MySQL string datatype, one might want to specify MySQL-specific arguments such as `charset` or `national`, which are available from the MySQL version of `VARCHAR` as the MySQL-only parameters `VARCHAR.charset` and `VARCHAR.national`.

API documentation for backend-specific types are in the dialect-specific documentation, listed at Dialects.

## Using “UPPERCASE” and Backend-specific types for multiple backends

Reviewing the presence of “UPPERCASE” and “CamelCase” types leads to the natural use case of how to make use of “UPPERCASE” datatypes for backend-specific options, but only when that backend is in use. To tie together the database-agnostic “CamelCase” and backend-specific “UPPERCASE” systems, one makes use of the `TypeEngine.with_variant()` method in order to compose types together to work with specific behaviors on specific backends.

Such as, to use the `String` datatype, but when running on MySQL to make use of the `VARCHAR.charset` parameter of `VARCHAR` when the table is created on MySQL, `TypeEngine.with_variant()` may be used as below:

    from sqlalchemy import MetaData
    from sqlalchemy import Table, Column, Integer, String
    from sqlalchemy.dialects.mysql import VARCHAR

    metadata_obj = MetaData()

    user = Table(
        "user",
        metadata_obj,
        Column("user_name", String(100), primary_key=True),
        Column(
            "bio",
            String(255).with_variant(VARCHAR(255, charset="utf8"), "mysql"),
        ),
    )

In the above table definition, the `"bio"` column will have string-behaviors on all backends. On most backends it will render in DDL as `VARCHAR`. However on MySQL (indicated by database URLs that start with `mysql`), it will render as `VARCHAR(255) CHARACTER SET utf8`.

See also

`TypeEngine.with_variant()` - additional usage examples and notes

## Generic “CamelCase” Types

Generic types specify a column that can read, write and store a particular type of Python data. SQLAlchemy will choose the best database column type available on the target database when issuing a `CREATE TABLE` statement. For complete control over which column type is emitted in `CREATE TABLE`, such as `VARCHAR` see SQL Standard and Multiple Vendor “UPPERCASE” Types and the other sections of this chapter.

Object Name | Description
--- | ---
BigInteger | A type for bigger `int` integers.
Boolean | A bool datatype.
Date | A type for `datetime.date()` objects.
DateTime | A type for `datetime.datetime()` objects.
Enum | Generic Enum Type.
Float | Type representing floating point types, such as `FLOAT` or `REAL`.
Integer | A type for `int` integers.
Interval | A type for `datetime.timedelta()` objects.
LargeBinary | A type for large binary byte data.
MatchType | Refers to the return type of the MATCH operator.
Numeric | Base for non-integer numeric types, such as `NUMERIC`, `FLOAT`, `DECIMAL`, and other variants.
PickleType | Holds Python objects, which are serialized using pickle.
SchemaType | Mark a type as possibly requiring schema-level DDL for usage.
SmallInteger | A type for smaller `int` integers.
String | The base for all string and character types.
Text | A variably sized string type.
Time | A type for `datetime.time()` objects.
Unicode | A variable length Unicode string type.
UnicodeText | An unbounded-length Unicode string type.

class sqlalchemy.types.BigInteger

  A type for bigger `int` integers.

  Typically generates a `BIGINT` in DDL, and otherwise acts like a normal `Integer` on the Python side.

  Class signature

  class `sqlalchemy.types.BigInteger` (`sqlalchemy.types.Integer`)

class sqlalchemy.types.Boolean(create_constraint=False, name=None, _create_events=True)

  A bool datatype.

  `Boolean` typically uses BOOLEAN or SMALLINT on the DDL side, and on the Python side deals in `True` or `False`.

  The `Boolean` datatype currently has two levels of assertion that the values persisted are simple true/false values. For all backends, only the Python values `None`, `True`, `False`, `1` or `0` are accepted as parameter values. For those backends that don’t support a “native boolean” datatype, an option exists to also create a CHECK constraint on the target column

  Changed in version 1.2: the `Boolean` datatype now asserts that incoming Python values are already in pure boolean form.

  Members

  __init__(), bind_processor(), literal_processor(), python_type, result_processor()

  Class signature

  class `sqlalchemy.types.Boolean` (`sqlalchemy.types.Emulated`, `sqlalchemy.types.TypeEngine`, `sqlalchemy.types.SchemaType`)

  method `sqlalchemy.types.Boolean.`__init__(create_constraint=False, name=None, _create_events=True)

    Construct a Boolean.

    Parameters:

      - create_constraint –

        defaults to False. If the boolean is generated as an int/smallint, also create a CHECK constraint on the table that ensures 1 or 0 as a value.

        Note

        it is strongly recommended that the CHECK constraint have an explicit name in order to support schema-management concerns. This can be established either by setting the `Boolean.name` parameter or by setting up an appropriate naming convention; see Configuring Constraint Naming Conventions for background.

        Changed in version 1.4: - this flag now defaults to False, meaning no CHECK constraint is generated for a non-native enumerated type.

      - name – if a CHECK constraint is generated, specify the name of the constraint.

  method `sqlalchemy.types.Boolean.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  method `sqlalchemy.types.Boolean.`literal_processor(dialect)

    Return a conversion function for processing literal values that are to be rendered directly without using binds.

    This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

    Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.literal_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.literal_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_literal_param()`.

    See also

    Augmenting Existing Types

  attribute `sqlalchemy.types.Boolean.`python_type
  method `sqlalchemy.types.Boolean.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.Date

  A type for `datetime.date()` objects.

  Members

  get_dbapi_type(), python_type

  Class signature

  class `sqlalchemy.types.Date` (`sqlalchemy.types._LookupExpressionAdapter`, `sqlalchemy.types.TypeEngine`)

  method `sqlalchemy.types.Date.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  attribute `sqlalchemy.types.Date.`python_type

class sqlalchemy.types.DateTime(timezone=False)

  A type for `datetime.datetime()` objects.

  Date and time types return objects from the Python `datetime` module. Most DBAPIs have built in support for the datetime module, with the noted exception of SQLite. In the case of SQLite, date and time types are stored as strings which are then converted back to datetime objects when rows are returned.

  For the time representation within the datetime type, some backends include additional options, such as timezone support and fractional seconds support. For fractional seconds, use the dialect-specific datatype, such as `TIME`. For timezone support, use at least the `TIMESTAMP` datatype, if not the dialect-specific datatype object.

  Members

  __init__(), get_dbapi_type(), python_type

  Class signature

  class `sqlalchemy.types.DateTime` (`sqlalchemy.types._LookupExpressionAdapter`, `sqlalchemy.types.TypeEngine`)

  method `sqlalchemy.types.DateTime.`__init__(timezone=False)

    Construct a new `DateTime`.

    Parameters:

      timezone – boolean. Indicates that the datetime type should enable timezone support, if available on the base date/time-holding type only. It is recommended to make use of the `TIMESTAMP` datatype directly when using this flag, as some databases include separate generic date/time-holding types distinct from the timezone-capable TIMESTAMP datatype, such as Oracle.

  method `sqlalchemy.types.DateTime.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  attribute `sqlalchemy.types.DateTime.`python_type

class sqlalchemy.types.Enum(*enums, **kw)

  Generic Enum Type.

  The `Enum` type provides a set of possible string values which the column is constrained towards.

  The `Enum` type will make use of the backend’s native “ENUM” type if one is available; otherwise, it uses a VARCHAR datatype. An option also exists to automatically produce a CHECK constraint when the VARCHAR (so called “non-native”) variant is produced; see the `Enum.create_constraint` flag.

  The `Enum` type also provides in-Python validation of string values during both read and write operations. When reading a value from the database in a result set, the string value is always checked against the list of possible values and a `LookupError` is raised if no match is found. When passing a value to the database as a plain string within a SQL statement, if the `Enum.validate_strings` parameter is set to True, a `LookupError` is raised for any string value that’s not located in the given list of possible values; note that this impacts usage of LIKE expressions with enumerated values (an unusual use case).

  Changed in version 1.1: the `Enum` type now provides in-Python validation of input values as well as on data being returned by the database.

  The source of enumerated values may be a list of string values, or alternatively a PEP-435-compliant enumerated class. For the purposes of the `Enum` datatype, this class need only provide a `__members__` method.

  When using an enumerated class, the enumerated objects are used both for input and output, rather than strings as is the case with a plain-string enumerated type:

      import enum
      from sqlalchemy import Enum

      class MyEnum(enum.Enum):
          one = 1
          two = 2
          three = 3

      t = Table(
          'data', MetaData(),
          Column('value', Enum(MyEnum))
      )

      connection.execute(t.insert(), {"value": MyEnum.two})
      assert connection.scalar(t.select()) is MyEnum.two

  Above, the string names of each element, e.g. “one”, “two”, “three”, are persisted to the database; the values of the Python Enum, here indicated as integers, are not used; the value of each enum can therefore be any kind of Python object whether or not it is persistable.

  In order to persist the values and not the names, the `Enum.values_callable` parameter may be used. The value of this parameter is a user-supplied callable, which is intended to be used with a PEP-435-compliant enumerated class and returns a list of string values to be persisted. For a simple enumeration that uses string values, a callable such as `lambda x: [e.value for e in x]` is sufficient.

  New in version 1.1: - support for PEP-435-style enumerated classes.

  See also

  `ENUM` - PostgreSQL-specific type, which has additional functionality.

  `ENUM` - MySQL-specific type

  Members

  __init__(), create(), drop()

  Class signature

  class `sqlalchemy.types.Enum` (`sqlalchemy.types.Emulated`, `sqlalchemy.types.String`, `sqlalchemy.types.SchemaType`)

  method `sqlalchemy.types.Enum.`__init__(*enums, **kw)

    Construct an enum.

    Keyword arguments which don’t apply to a specific backend are ignored by that backend.

    Parameters:

      - *enums –

        either exactly one PEP-435 compliant enumerated type or one or more string labels.

        New in version 1.1: a PEP-435 style enumerated class may be passed.

      - convert_unicode –

        Enable unicode-aware bind parameter and result-set processing for this Enum’s data under Python 2 only. Under Python 2, this is set automatically based on the presence of unicode label strings. This flag will be removed in SQLAlchemy 2.0.

        Deprecated since version 1.3: The `Enum.convert_unicode` parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary.

      - create_constraint –

        defaults to False. When creating a non-native enumerated type, also build a CHECK constraint on the database against the valid values.

        Note

        it is strongly recommended that the CHECK constraint have an explicit name in order to support schema-management concerns. This can be established either by setting the `Enum.name` parameter or by setting up an appropriate naming convention; see Configuring Constraint Naming Conventions for background.

        Changed in version 1.4: - this flag now defaults to False, meaning no CHECK constraint is generated for a non-native enumerated type.

      - metadata –

        Associate this type directly with a `MetaData` object. For types that exist on the target database as an independent schema construct (PostgreSQL), this type will be created and dropped within `create_all()` and `drop_all()` operations. If the type is not associated with any `MetaData` object, it will associate itself with each `Table` in which it is used, and will be created when any of those individual tables are created, after a check is performed for its existence. The type is only dropped when `drop_all()` is called for that `Table` object’s metadata, however.

        The value of the `MetaData.schema` parameter of the `MetaData` object, if set, will be used as the default value of the `Enum.schema` on this object if an explicit value is not otherwise supplied.

        Changed in version 1.4.12: `Enum` inherits the `MetaData.schema` parameter of the `MetaData` object if present, when passed using the `Enum.metadata` parameter.

      - name – The name of this type. This is required for PostgreSQL and any future supported database which requires an explicitly named type, or an explicitly named constraint in order to generate the type and/or a table that uses it. If a PEP-435 enumerated class was used, its name (converted to lower case) is used by default.

      - native_enum – Use the database’s native ENUM type when available. Defaults to True. When False, uses VARCHAR + check constraint for all backends. When False, the VARCHAR length can be controlled with `Enum.length`; currently “length” is ignored if native_enum=True.

      - length –

        Allows specifying a custom length for the VARCHAR when `Enum.native_enum` is False. By default it uses the length of the longest value.

        New in version 1.3.16.

      - schema –

        Schema name of this type. For types that exist on the target database as an independent schema construct (PostgreSQL), this parameter specifies the named schema in which the type is present.

        If not present, the schema name will be taken from the `MetaData` collection if passed as `Enum.metadata`, for a `MetaData` that includes the `MetaData.schema` parameter.

        Changed in version 1.4.12: `Enum` inherits the `MetaData.schema` parameter of the `MetaData` object if present, when passed using the `Enum.metadata` parameter.

        Otherwise, if the `Enum.inherit_schema` flag is set to `True`, the schema will be inherited from the associated `Table` object if any; when `Enum.inherit_schema` is at its default of `False`, the owning table’s schema is not used.

      - quote – Set explicit quoting preferences for the type’s name.

      - inherit_schema – When `True`, the “schema” from the owning `Table` will be copied to the “schema” attribute of this `Enum`, replacing whatever value was passed for the `schema` attribute. This also takes effect when using the `Table.to_metadata()` operation.

      - validate_strings –

        when True, string values that are being passed to the database in a SQL statement will be checked for validity against the list of enumerated values. Unrecognized values will result in a `LookupError` being raised.

        New in version 1.1.0b2.

      - values_callable –

        A callable which will be passed the PEP-435 compliant enumerated type, which should then return a list of string values to be persisted. This allows for alternate usages such as using the string value of an enum to be persisted to the database instead of its name.

        New in version 1.2.3.

      - sort_key_function –

        a Python callable which may be used as the “key” argument in the Python `sorted()` built-in. The SQLAlchemy ORM requires that primary key columns which are mapped must be sortable in some way. When using an unsortable enumeration object such as a Python 3 `Enum` object, this parameter may be used to set a default sort key function for the objects. By default, the database value of the enumeration is used as the sorting function.

        New in version 1.3.8.

      - omit_aliases –

        A boolean that when true will remove aliases from pep 435 enums. For backward compatibility it defaults to `False`. A deprecation warning is raised if the enum has aliases and this flag was not set.

        New in version 1.4.5.

        Deprecated since version 1.4: The default will be changed to `True` in SQLAlchemy 2.0.

  method `sqlalchemy.types.Enum.`create(bind=None, checkfirst=False)

    inherited from the `SchemaType.create()` method of `SchemaType`

    Issue CREATE DDL for this type, if applicable.

  method `sqlalchemy.types.Enum.`drop(bind=None, checkfirst=False)

    inherited from the `SchemaType.drop()` method of `SchemaType`

    Issue DROP DDL for this type, if applicable.

class sqlalchemy.types.Float(precision=None, asdecimal=False, decimal_return_scale=None)

  Type representing floating point types, such as `FLOAT` or `REAL`.

  This type returns Python `float` objects by default, unless the `Float.asdecimal` flag is set to True, in which case they are coerced to `decimal.Decimal` objects.

  Members

  __init__(), result_processor()

  Class signature

  class `sqlalchemy.types.Float` (`sqlalchemy.types.Numeric`)

  method `sqlalchemy.types.Float.`__init__(precision=None, asdecimal=False, decimal_return_scale=None)

    Construct a Float.

    Parameters:

      - precision – the numeric precision for use in DDL `CREATE TABLE`.

      - asdecimal – the same flag as that of `Numeric`, but defaults to `False`. Note that setting this flag to `True` results in floating point conversion.

      - decimal_return_scale –

        Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.

        New in version 0.9.0.

  method `sqlalchemy.types.Float.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.Integer

  A type for `int` integers.

  Members

  get_dbapi_type(), literal_processor(), python_type

  Class signature

  class `sqlalchemy.types.Integer` (`sqlalchemy.types._LookupExpressionAdapter`, `sqlalchemy.types.TypeEngine`)

  method `sqlalchemy.types.Integer.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  method `sqlalchemy.types.Integer.`literal_processor(dialect)

    Return a conversion function for processing literal values that are to be rendered directly without using binds.

    This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

    Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.literal_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.literal_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_literal_param()`.

    See also

    Augmenting Existing Types

  attribute `sqlalchemy.types.Integer.`python_type

class sqlalchemy.types.Interval(native=True, second_precision=None, day_precision=None)

  A type for `datetime.timedelta()` objects.

  The Interval type deals with `datetime.timedelta` objects. In PostgreSQL, the native `INTERVAL` type is used; for others, the value is stored as a date which is relative to the “epoch” (Jan. 1, 1970).

  Note that the `Interval` type does not currently provide date arithmetic operations on platforms which do not support interval types natively. Such operations usually require transformation of both sides of the expression (such as, conversion of both sides into integer epoch values first) which currently is a manual procedure (such as via `expression.func`).

  Members

  __init__(), adapt_to_emulated(), bind_processor(), cache_ok, impl, python_type, result_processor()

  Class signature

  class `sqlalchemy.types.Interval` (`sqlalchemy.types.Emulated`, `sqlalchemy.types._AbstractInterval`, `sqlalchemy.types.TypeDecorator`)

  method `sqlalchemy.types.Interval.`__init__(native=True, second_precision=None, day_precision=None)

    Construct an Interval object.

    Parameters:

      - native – when True, use the actual INTERVAL type provided by the database, if supported (currently PostgreSQL, Oracle). Otherwise, represent the interval data as an epoch value regardless.

      - second_precision – For native interval types which support a “fractional seconds precision” parameter, i.e. Oracle and PostgreSQL

      - day_precision – for native interval types which support a “day precision” parameter, i.e. Oracle.

  method `sqlalchemy.types.Interval.`adapt_to_emulated(impltype, **kw)

    Given an impl class, adapt this type to the impl assuming “emulated”.

    The impl should also be an “emulated” version of this type, most likely the same class as this type itself.

    e.g.: sqltypes.Enum adapts to the Enum class.

  method `sqlalchemy.types.Interval.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  attribute `sqlalchemy.types.Interval.`cache_ok = True

    Indicate if statements using this `ExternalType` are “safe to cache”.

    The default value `None` will emit a warning and then not allow caching of a statement which includes this type. Set to `False` to disable statements using this type from being cached at all without a warning. When set to `True`, the object’s class and selected elements from its state will be used as part of the cache key. For example, using a `TypeDecorator`:

        class MyType(TypeDecorator):
            impl = String

            cache_ok = True

            def __init__(self, choices):
                self.choices = tuple(choices)
                self.internal_only = True

    The cache key for the above type would be equivalent to:

        >>> MyType(["a", "b", "c"])._static_cache_key
        (<class '__main__.MyType'>, ('choices', ('a', 'b', 'c')))

    The caching scheme will extract attributes from the type that correspond to the names of parameters in the `__init__()` method. Above, the “choices” attribute becomes part of the cache key but “internal_only” does not, because there is no parameter named “internal_only”.

    The requirements for cacheable elements is that they are hashable and also that they indicate the same SQL rendered for expressions using this type every time for a given cache value.

    To accommodate for datatypes that refer to unhashable structures such as dictionaries, sets and lists, these objects can be made “cacheable” by assigning hashable structures to the attributes whose names correspond with the names of the arguments. For example, a datatype which accepts a dictionary of lookup values may publish this as a sorted series of tuples. Given a previously un-cacheable type as:

        class LookupType(UserDefinedType):
            '''a custom type that accepts a dictionary as a parameter.

            this is the non-cacheable version, as "self.lookup" is not
            hashable.

            '''

            def __init__(self, lookup):
                self.lookup = lookup

            def get_col_spec(self, **kw):
                return "VARCHAR(255)"

            def bind_processor(self, dialect):
                # ...  works with "self.lookup" ...

    Where “lookup” is a dictionary. The type will not be able to generate a cache key:

        >>> type_ = LookupType({"a": 10, "b": 20})
        >>> type_._static_cache_key
        <stdin>:1: SAWarning: UserDefinedType LookupType({'a': 10, 'b': 20}) will not
        produce a cache key because the ``cache_ok`` flag is not set to True.
        Set this flag to True if this type object's state is safe to use
        in a cache key, or False to disable this warning.
        symbol('no_cache')

    If we did set up such a cache key, it wouldn’t be usable. We would get a tuple structure that contains a dictionary inside of it, which cannot itself be used as a key in a “cache dictionary” such as SQLAlchemy’s statement cache, since Python dictionaries aren’t hashable:

        >>> # set cache_ok = True
        >>> type_.cache_ok = True

        >>> # this is the cache key it would generate
        >>> key = type_._static_cache_key
        >>> key
        (<class '__main__.LookupType'>, ('lookup', {'a': 10, 'b': 20}))

        >>> # however this key is not hashable, will fail when used with
        >>> # SQLAlchemy statement cache
        >>> some_cache = {key: "some sql value"}
        Traceback (most recent call last): File "<stdin>", line 1,
        in <module> TypeError: unhashable type: 'dict'

    The type may be made cacheable by assigning a sorted tuple of tuples to the “.lookup” attribute:

        class LookupType(UserDefinedType):
            '''a custom type that accepts a dictionary as a parameter.

            The dictionary is stored both as itself in a private variable,
            and published in a public variable as a sorted tuple of tuples,
            which is hashable and will also return the same value for any
            two equivalent dictionaries.  Note it assumes the keys and
            values of the dictionary are themselves hashable.

            '''

            cache_ok = True

            def __init__(self, lookup):
                self._lookup = lookup

                # assume keys/values of "lookup" are hashable; otherwise
                # they would also need to be converted in some way here
                self.lookup = tuple(
                    (key, lookup[key]) for key in sorted(lookup)
                )

            def get_col_spec(self, **kw):
                return "VARCHAR(255)"

            def bind_processor(self, dialect):
                # ...  works with "self._lookup" ...

    Where above, the cache key for `LookupType({"a": 10, "b": 20})` will be:

        >>> LookupType({"a": 10, "b": 20})._static_cache_key
        (<class '__main__.LookupType'>, ('lookup', (('a', 10), ('b', 20))))

    New in version 1.4.14: - added the `cache_ok` flag to allow some configurability of caching for `TypeDecorator` classes.

    New in version 1.4.28: - added the `ExternalType` mixin which generalizes the `cache_ok` flag to both the `TypeDecorator` and `UserDefinedType` classes.

    See also

    SQL Compilation Caching

  attribute `sqlalchemy.types.Interval.`impl

    alias of `DateTime`

  attribute `sqlalchemy.types.Interval.`python_type
  method `sqlalchemy.types.Interval.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.LargeBinary(length=None)

  A type for large binary byte data.

  The `LargeBinary` type corresponds to a large and/or unlengthed binary type for the target platform, such as BLOB on MySQL and BYTEA for PostgreSQL. It also handles the necessary conversions for the DBAPI.

  Members

  __init__()

  Class signature

  class `sqlalchemy.types.LargeBinary` (`sqlalchemy.types._Binary`)

  method `sqlalchemy.types.LargeBinary.`__init__(length=None)

    Construct a LargeBinary type.

    Parameters:

      length – optional, a length for the column for use in DDL statements, for those binary types that accept a length, such as the MySQL BLOB type.

class sqlalchemy.types.MatchType(create_constraint=False, name=None, _create_events=True)

  Refers to the return type of the MATCH operator.

  As the `ColumnOperators.match()` is probably the most open-ended operator in generic SQLAlchemy Core, we can’t assume the return type at SQL evaluation time, as MySQL returns a floating point, not a boolean, and other backends might do something different. So this type acts as a placeholder, currently subclassing `Boolean`. The type allows dialects to inject result-processing functionality if needed, and on MySQL will return floating-point values.

  New in version 1.0.0.

  Class signature

  class `sqlalchemy.types.MatchType` (`sqlalchemy.types.Boolean`)

class sqlalchemy.types.Numeric(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

  Base for non-integer numeric types, such as `NUMERIC`, `FLOAT`, `DECIMAL`, and other variants.

  The `Numeric` datatype when used directly will render DDL corresponding to precision numerics if available, such as `NUMERIC(precision, scale)`. The `Float` subclass will attempt to render a floating-point datatype such as `FLOAT(precision)`.

  `Numeric` returns Python `decimal.Decimal` objects by default, based on the default value of `True` for the `Numeric.asdecimal` parameter. If this parameter is set to False, returned values are coerced to Python `float` objects.

  The `Float` subtype, being more specific to floating point, defaults the `Float.asdecimal` flag to False so that the default Python datatype is `float`.

  Note

  When using a `Numeric` datatype against a database type that returns Python floating point values to the driver, the accuracy of the decimal conversion indicated by `Numeric.asdecimal` may be limited. The behavior of specific numeric/floating point datatypes is a product of the SQL datatype in use, the Python DBAPI in use, as well as strategies that may be present within the SQLAlchemy dialect in use. Users requiring specific precision/ scale are encouraged to experiment with the available datatypes in order to determine the best results.

  Members

  __init__(), bind_processor(), get_dbapi_type(), literal_processor(), python_type, result_processor()

  Class signature

  class `sqlalchemy.types.Numeric` (`sqlalchemy.types._LookupExpressionAdapter`, `sqlalchemy.types.TypeEngine`)

  method `sqlalchemy.types.Numeric.`__init__(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

    Construct a Numeric.

    Parameters:

      - precision – the numeric precision for use in DDL `CREATE TABLE`.

      - scale – the numeric scale for use in DDL `CREATE TABLE`.

      - asdecimal – default True. Return whether or not values should be sent as Python Decimal objects, or as floats. Different DBAPIs send one or the other based on datatypes - the Numeric type will ensure that return values are one or the other across DBAPIs consistently.

      - decimal_return_scale – Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Types which do include an explicit “.scale” value, such as the base `Numeric` as well as the MySQL float types, will use the value of “.scale” as the default for decimal_return_scale, if not otherwise specified.

    When using the `Numeric` type, care should be taken to ensure that the asdecimal setting is appropriate for the DBAPI in use - when Numeric applies a conversion from Decimal->float or float-> Decimal, this conversion incurs an additional performance overhead for all result columns received.

    DBAPIs that return Decimal natively (e.g. psycopg2) will have better accuracy and higher performance with a setting of `True`, as the native translation to Decimal reduces the amount of floating- point issues at play, and the Numeric type itself doesn’t need to apply any further conversions. However, another DBAPI which returns floats natively will incur an additional conversion overhead, and is still subject to floating point data loss - in which case `asdecimal=False` will at least remove the extra conversion overhead.

  method `sqlalchemy.types.Numeric.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  method `sqlalchemy.types.Numeric.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  method `sqlalchemy.types.Numeric.`literal_processor(dialect)

    Return a conversion function for processing literal values that are to be rendered directly without using binds.

    This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

    Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.literal_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.literal_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_literal_param()`.

    See also

    Augmenting Existing Types

  attribute `sqlalchemy.types.Numeric.`python_type
  method `sqlalchemy.types.Numeric.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.PickleType(protocol=5, pickler=None, comparator=None, impl=None)

  Holds Python objects, which are serialized using pickle.

  PickleType builds upon the Binary type to apply Python’s `pickle.dumps()` to incoming objects, and `pickle.loads()` on the way out, allowing any pickleable Python object to be stored as a serialized binary field.

  To allow ORM change events to propagate for elements associated with `PickleType`, see Mutation Tracking.

  Members

  __init__(), bind_processor(), cache_ok, compare_values(), impl, result_processor()

  Class signature

  class `sqlalchemy.types.PickleType` (`sqlalchemy.types.TypeDecorator`)

  method `sqlalchemy.types.PickleType.`__init__(protocol=5, pickler=None, comparator=None, impl=None)

    Construct a PickleType.

    Parameters:

      - protocol – defaults to `pickle.HIGHEST_PROTOCOL`.

      - pickler – defaults to cPickle.pickle or pickle.pickle if cPickle is not available. May be any object with pickle-compatible `dumps` and `loads` methods.

      - comparator – a 2-arg callable predicate used to compare values of this type. If left as `None`, the Python “equals” operator is used to compare values.

      - impl –

        A binary-storing `TypeEngine` class or instance to use in place of the default `LargeBinary`. For example the :class: _mysql.LONGBLOB class may be more effective when using MySQL.

        New in version 1.4.20.

  method `sqlalchemy.types.PickleType.`bind_processor(dialect)

    Provide a bound value processing function for the given `Dialect`.

    This is the method that fulfills the `TypeEngine` contract for bound value conversion which normally occurs via the `TypeEngine.bind_processor()` method.

    Note

    User-defined subclasses of `TypeDecorator` should not implement this method, and should instead implement `TypeDecorator.process_bind_param()` so that the “inner” processing provided by the implementing type is maintained.

    Parameters:

      dialect – Dialect instance in use.

  attribute `sqlalchemy.types.PickleType.`cache_ok = True

    Indicate if statements using this `ExternalType` are “safe to cache”.

    The default value `None` will emit a warning and then not allow caching of a statement which includes this type. Set to `False` to disable statements using this type from being cached at all without a warning. When set to `True`, the object’s class and selected elements from its state will be used as part of the cache key. For example, using a `TypeDecorator`:

        class MyType(TypeDecorator):
            impl = String

            cache_ok = True

            def __init__(self, choices):
                self.choices = tuple(choices)
                self.internal_only = True

    The cache key for the above type would be equivalent to:

        >>> MyType(["a", "b", "c"])._static_cache_key
        (<class '__main__.MyType'>, ('choices', ('a', 'b', 'c')))

    The caching scheme will extract attributes from the type that correspond to the names of parameters in the `__init__()` method. Above, the “choices” attribute becomes part of the cache key but “internal_only” does not, because there is no parameter named “internal_only”.

    The requirements for cacheable elements is that they are hashable and also that they indicate the same SQL rendered for expressions using this type every time for a given cache value.

    To accommodate for datatypes that refer to unhashable structures such as dictionaries, sets and lists, these objects can be made “cacheable” by assigning hashable structures to the attributes whose names correspond with the names of the arguments. For example, a datatype which accepts a dictionary of lookup values may publish this as a sorted series of tuples. Given a previously un-cacheable type as:

        class LookupType(UserDefinedType):
            '''a custom type that accepts a dictionary as a parameter.

            this is the non-cacheable version, as "self.lookup" is not
            hashable.

            '''

            def __init__(self, lookup):
                self.lookup = lookup

            def get_col_spec(self, **kw):
                return "VARCHAR(255)"

            def bind_processor(self, dialect):
                # ...  works with "self.lookup" ...

    Where “lookup” is a dictionary. The type will not be able to generate a cache key:

        >>> type_ = LookupType({"a": 10, "b": 20})
        >>> type_._static_cache_key
        <stdin>:1: SAWarning: UserDefinedType LookupType({'a': 10, 'b': 20}) will not
        produce a cache key because the ``cache_ok`` flag is not set to True.
        Set this flag to True if this type object's state is safe to use
        in a cache key, or False to disable this warning.
        symbol('no_cache')

    If we did set up such a cache key, it wouldn’t be usable. We would get a tuple structure that contains a dictionary inside of it, which cannot itself be used as a key in a “cache dictionary” such as SQLAlchemy’s statement cache, since Python dictionaries aren’t hashable:

        >>> # set cache_ok = True
        >>> type_.cache_ok = True

        >>> # this is the cache key it would generate
        >>> key = type_._static_cache_key
        >>> key
        (<class '__main__.LookupType'>, ('lookup', {'a': 10, 'b': 20}))

        >>> # however this key is not hashable, will fail when used with
        >>> # SQLAlchemy statement cache
        >>> some_cache = {key: "some sql value"}
        Traceback (most recent call last): File "<stdin>", line 1,
        in <module> TypeError: unhashable type: 'dict'

    The type may be made cacheable by assigning a sorted tuple of tuples to the “.lookup” attribute:

        class LookupType(UserDefinedType):
            '''a custom type that accepts a dictionary as a parameter.

            The dictionary is stored both as itself in a private variable,
            and published in a public variable as a sorted tuple of tuples,
            which is hashable and will also return the same value for any
            two equivalent dictionaries.  Note it assumes the keys and
            values of the dictionary are themselves hashable.

            '''

            cache_ok = True

            def __init__(self, lookup):
                self._lookup = lookup

                # assume keys/values of "lookup" are hashable; otherwise
                # they would also need to be converted in some way here
                self.lookup = tuple(
                    (key, lookup[key]) for key in sorted(lookup)
                )

            def get_col_spec(self, **kw):
                return "VARCHAR(255)"

            def bind_processor(self, dialect):
                # ...  works with "self._lookup" ...

    Where above, the cache key for `LookupType({"a": 10, "b": 20})` will be:

        >>> LookupType({"a": 10, "b": 20})._static_cache_key
        (<class '__main__.LookupType'>, ('lookup', (('a', 10), ('b', 20))))

    New in version 1.4.14: - added the `cache_ok` flag to allow some configurability of caching for `TypeDecorator` classes.

    New in version 1.4.28: - added the `ExternalType` mixin which generalizes the `cache_ok` flag to both the `TypeDecorator` and `UserDefinedType` classes.

    See also

    SQL Compilation Caching

  method `sqlalchemy.types.PickleType.`compare_values(x, y)

    Given two values, compare them for equality.

    By default this calls upon `TypeEngine.compare_values()` of the underlying “impl”, which in turn usually uses the Python equals operator `==`.

    This function is used by the ORM to compare an original-loaded value with an intercepted “changed” value, to determine if a net change has occurred.

  attribute `sqlalchemy.types.PickleType.`impl

    alias of `LargeBinary`

  method `sqlalchemy.types.PickleType.`result_processor(dialect, coltype)

    Provide a result value processing function for the given `Dialect`.

    This is the method that fulfills the `TypeEngine` contract for bound value conversion which normally occurs via the `TypeEngine.result_processor()` method.

    Note

    User-defined subclasses of `TypeDecorator` should not implement this method, and should instead implement `TypeDecorator.process_result_value()` so that the “inner” processing provided by the implementing type is maintained.

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – A SQLAlchemy data type

class sqlalchemy.types.SchemaType(name=None, schema=None, metadata=None, inherit_schema=False, quote=None, _create_events=True)

  Mark a type as possibly requiring schema-level DDL for usage.

  Supports types that must be explicitly created/dropped (i.e. PG ENUM type) as well as types that are complimented by table or schema level constraints, triggers, and other rules.

  `SchemaType` classes can also be targets for the `DDLEvents.before_parent_attach()` and `DDLEvents.after_parent_attach()` events, where the events fire off surrounding the association of the type object with a parent `Column`.

  See also

  `Enum`

  `Boolean`

  Members

  adapt(), bind, copy(), create(), drop()

  Class signature

  class `sqlalchemy.types.SchemaType` (`sqlalchemy.sql.expression.SchemaEventTarget`)

  method `sqlalchemy.types.SchemaType.`adapt(impltype, **kw)
  attribute `sqlalchemy.types.SchemaType.`bind
  method `sqlalchemy.types.SchemaType.`copy(**kw)
  method `sqlalchemy.types.SchemaType.`create(bind=None, checkfirst=False)

    Issue CREATE DDL for this type, if applicable.

  method `sqlalchemy.types.SchemaType.`drop(bind=None, checkfirst=False)

    Issue DROP DDL for this type, if applicable.

class sqlalchemy.types.SmallInteger

  A type for smaller `int` integers.

  Typically generates a `SMALLINT` in DDL, and otherwise acts like a normal `Integer` on the Python side.

  Class signature

  class `sqlalchemy.types.SmallInteger` (`sqlalchemy.types.Integer`)

class sqlalchemy.types.String(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  The base for all string and character types.

  In SQL, corresponds to VARCHAR. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.)

  The length field is usually required when the String type is used within a CREATE TABLE statement, as VARCHAR requires a length on most databases.

  Members

  RETURNS_BYTES, RETURNS_CONDITIONAL, RETURNS_UNICODE, RETURNS_UNKNOWN, __init__(), bind_processor(), get_dbapi_type(), literal_processor(), python_type, result_processor()

  Class signature

  class `sqlalchemy.types.String` (`sqlalchemy.types.Concatenable`, `sqlalchemy.types.TypeEngine`)

  attribute `sqlalchemy.types.String.`RETURNS_BYTES = symbol('RETURNS_BYTES')
  attribute `sqlalchemy.types.String.`RETURNS_CONDITIONAL = symbol('RETURNS_CONDITIONAL')
  attribute `sqlalchemy.types.String.`RETURNS_UNICODE = symbol('RETURNS_UNICODE')
  attribute `sqlalchemy.types.String.`RETURNS_UNKNOWN = symbol('RETURNS_UNKNOWN')
  method `sqlalchemy.types.String.`__init__(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

    Create a string-holding type.

    Parameters:

      - length – optional, a length for the column for use in DDL and CAST expressions. May be safely omitted if no `CREATE TABLE` will be issued. Certain databases may require a `length` for use in DDL, and will raise an exception when the `CREATE TABLE` DDL is issued if a `VARCHAR` with no length is included. Whether the value is interpreted as bytes or characters is database specific.

      - collation –

        Optional, a column-level collation for use in DDL and CAST expressions. Renders using the COLLATE keyword supported by SQLite, MySQL, and PostgreSQL. E.g.:

            >>> from sqlalchemy import cast, select, String
            >>> print(select(cast('some string', String(collation='utf8'))))
            SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1

      - convert_unicode –

        When set to `True`, the `String` type will assume that input is to be passed as Python Unicode objects under Python 2, and results returned as Python Unicode objects. In the rare circumstance that the DBAPI does not support Python unicode under Python 2, SQLAlchemy will use its own encoder/decoder functionality on strings, referring to the value of the `create_engine.encoding` parameter parameter passed to `create_engine()` as the encoding.

        Deprecated since version 1.3: The `String.convert_unicode` parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary.

        For the extremely rare case that Python Unicode is to be encoded/decoded by SQLAlchemy on a backend that does natively support Python Unicode, the string value `"force"` can be passed here which will cause SQLAlchemy’s encode/decode services to be used unconditionally.

        Note

        SQLAlchemy’s unicode-conversion flags and features only apply to Python 2; in Python 3, all string objects are Unicode objects. For this reason, as well as the fact that virtually all modern DBAPIs now support Unicode natively even under Python 2, the `String.convert_unicode` flag is inherently a legacy feature.

        Note

        In the vast majority of cases, the `Unicode` or `UnicodeText` datatypes should be used for a `Column` that expects to store non-ascii data. These datatypes will ensure that the correct types are used on the database side as well as set up the correct Unicode behaviors under Python 2.

        See also

        `create_engine.convert_unicode` - `Engine`-wide parameter

      - unicode_error –

        Optional, a method to use to handle Unicode conversion errors. Behaves like the `errors` keyword argument to the standard library’s `string.decode()` functions, requires that `String.convert_unicode` is set to `"force"`

        Deprecated since version 1.3: The `String.unicode_errors` parameter is deprecated and will be removed in a future release. This parameter is unnecessary for modern Python DBAPIs and degrades performance significantly.

  method `sqlalchemy.types.String.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  method `sqlalchemy.types.String.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  method `sqlalchemy.types.String.`literal_processor(dialect)

    Return a conversion function for processing literal values that are to be rendered directly without using binds.

    This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

    Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.literal_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.literal_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_literal_param()`.

    See also

    Augmenting Existing Types

  attribute `sqlalchemy.types.String.`python_type
  method `sqlalchemy.types.String.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.types.Text(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  A variably sized string type.

  In SQL, usually corresponds to CLOB or TEXT. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.) In general, TEXT objects do not have a length; while some databases will accept a length argument here, it will be rejected by others.

  Class signature

  class `sqlalchemy.types.Text` (`sqlalchemy.types.String`)

class sqlalchemy.types.Time(timezone=False)

  A type for `datetime.time()` objects.

  Members

  get_dbapi_type(), python_type

  Class signature

  class `sqlalchemy.types.Time` (`sqlalchemy.types._LookupExpressionAdapter`, `sqlalchemy.types.TypeEngine`)

  method `sqlalchemy.types.Time.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

  attribute `sqlalchemy.types.Time.`python_type

class sqlalchemy.types.Unicode(length=None, **kwargs)

  A variable length Unicode string type.

  The `Unicode` type is a `String` subclass that assumes input and output strings that may contain non-ASCII characters, and for some backends implies an underlying column type that is explicitly supporting of non-ASCII data, such as `NVARCHAR` on Oracle and SQL Server. This will impact the output of `CREATE TABLE` statements and `CAST` functions at the dialect level, and also in some cases will indicate different behavior in the DBAPI itself in how it handles bound parameters.

  The character encoding used by the `Unicode` type that is used to transmit and receive data to the database is usually determined by the DBAPI itself. All modern DBAPIs accommodate non-ASCII strings but may have different methods of managing database encodings; if necessary, this encoding should be configured as detailed in the notes for the target DBAPI in the Dialects section.

  In modern SQLAlchemy, use of the `Unicode` datatype does not typically imply any encoding/decoding behavior within SQLAlchemy itself. Historically, when DBAPIs did not support Python `unicode` objects under Python 2, SQLAlchemy handled unicode encoding/decoding services itself which would be controlled by the flag `String.convert_unicode`; this flag is deprecated as it is no longer needed for Python 3.

  When using Python 2, data that is passed to columns that use the `Unicode` datatype must be of type `unicode`, and not `str` which in Python 2 is equivalent to `bytes`. In Python 3, all data passed to columns that use the `Unicode` datatype should be of type `str`. See the flag `String.convert_unicode` for more discussion of unicode encode/decode behavior under Python 2.

  Warning

  Some database backends, particularly SQL Server with pyodbc, are known to have undesirable behaviors regarding data that is noted as being of `NVARCHAR` type as opposed to `VARCHAR`, including datatype mismatch errors and non-use of indexes. See the section on `DialectEvents.do_setinputsizes()` for background on working around unicode character issues for backends like SQL Server with pyodbc as well as cx_Oracle.

  See also

  `UnicodeText` - unlengthed textual counterpart to `Unicode`.

  `String.convert_unicode`

  `DialectEvents.do_setinputsizes()`

  Members

  __init__()

  Class signature

  class `sqlalchemy.types.Unicode` (`sqlalchemy.types.String`)

  method `sqlalchemy.types.Unicode.`__init__(length=None, **kwargs)

    Create a `Unicode` object.

    Parameters are the same as that of `String`, with the exception that `convert_unicode` defaults to `True`.

class sqlalchemy.types.UnicodeText(length=None, **kwargs)

  An unbounded-length Unicode string type.

  See `Unicode` for details on the unicode behavior of this object.

  Like `Unicode`, usage the `UnicodeText` type implies a unicode-capable type being used on the backend, such as `NCLOB`, `NTEXT`.

  Members

  __init__()

  Class signature

  class `sqlalchemy.types.UnicodeText` (`sqlalchemy.types.Text`)

  method `sqlalchemy.types.UnicodeText.`__init__(length=None, **kwargs)

    Create a Unicode-converting Text type.

    Parameters are the same as that of `TextClause`, with the exception that `convert_unicode` defaults to `True`.

## SQL Standard and Multiple Vendor “UPPERCASE” Types

This category of types refers to types that are either part of the SQL standard, or are potentially found within a subset of database backends. Unlike the “generic” types, the SQL standard/multi-vendor types have no guarantee of working on all backends, and will only work on those backends that explicitly support them by name. That is, the type will always emit its exact name in DDL with `CREATE TABLE` is issued.

Object Name | Description
--- | ---
ARRAY | Represent a SQL Array type.
BIGINT | The SQL BIGINT type.
BINARY | The SQL BINARY type.
BLOB | The SQL BLOB type.
BOOLEAN | The SQL BOOLEAN type.
CHAR | The SQL CHAR type.
CLOB | The CLOB type.
DATE | The SQL DATE type.
DATETIME | The SQL DATETIME type.
DECIMAL | The SQL DECIMAL type.
FLOAT | The SQL FLOAT type.
INT | alias of `INTEGER`
INTEGER | The SQL INT or INTEGER type.
JSON | Represent a SQL JSON type.
NCHAR | The SQL NCHAR type.
NUMERIC | The SQL NUMERIC type.
NVARCHAR | The SQL NVARCHAR type.
REAL | The SQL REAL type.
SMALLINT | The SQL SMALLINT type.
TEXT | The SQL TEXT type.
TIME | The SQL TIME type.
TIMESTAMP | The SQL TIMESTAMP type.
VARBINARY | The SQL VARBINARY type.
VARCHAR | The SQL VARCHAR type.

class sqlalchemy.types.ARRAY(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

  Represent a SQL Array type.

  Note

  This type serves as the basis for all ARRAY operations. However, currently only the PostgreSQL backend has support for SQL arrays in SQLAlchemy. It is recommended to use the PostgreSQL-specific `sqlalchemy.dialects.postgresql.ARRAY` type directly when using ARRAY types with PostgreSQL, as it provides additional operators specific to that backend.

  `ARRAY` is part of the Core in support of various SQL standard functions such as `array_agg` which explicitly involve arrays; however, with the exception of the PostgreSQL backend and possibly some third-party dialects, no other SQLAlchemy built-in dialect has support for this type.

  An `ARRAY` type is constructed given the “type” of element:

      mytable = Table("mytable", metadata,
              Column("data", ARRAY(Integer))
          )

  The above type represents an N-dimensional array, meaning a supporting backend such as PostgreSQL will interpret values with any number of dimensions automatically. To produce an INSERT construct that passes in a 1-dimensional array of integers:

      connection.execute(
              mytable.insert(),
              {"data": [1,2,3]}
      )

  The `ARRAY` type can be constructed given a fixed number of dimensions:

      mytable = Table("mytable", metadata,
              Column("data", ARRAY(Integer, dimensions=2))
          )

  Sending a number of dimensions is optional, but recommended if the datatype is to represent arrays of more than one dimension. This number is used:

  - When emitting the type declaration itself to the database, e.g. `INTEGER[][]`

  - When translating Python values to database values, and vice versa, e.g. an ARRAY of `Unicode` objects uses this number to efficiently access the string values inside of array structures without resorting to per-row type inspection

  - When used with the Python `getitem` accessor, the number of dimensions serves to define the kind of type that the `[]` operator should return, e.g. for an ARRAY of INTEGER with two dimensions:

        >>> expr = table.c.column[5]  # returns ARRAY(Integer, dimensions=1)
        >>> expr = expr[6]  # returns Integer

  For 1-dimensional arrays, an `ARRAY` instance with no dimension parameter will generally assume single-dimensional behaviors.

  SQL expressions of type `ARRAY` have support for “index” and “slice” behavior. The Python `[]` operator works normally here, given integer indexes or slices. Arrays default to 1-based indexing. The operator produces binary expression constructs which will produce the appropriate SQL, both for SELECT statements:

      select(mytable.c.data[5], mytable.c.data[2:7])

  as well as UPDATE statements when the `Update.values()` method is used:

      mytable.update().values({
          mytable.c.data[5]: 7,
          mytable.c.data[2:7]: [1, 2, 3]
      })

  The `ARRAY` type also provides for the operators `Comparator.any()` and `Comparator.all()`. The PostgreSQL-specific version of `ARRAY` also provides additional operators.

  Detecting Changes in ARRAY columns when using the ORM

  The `ARRAY` type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the array. In order to detect these, the `sqlalchemy.ext.mutable` extension must be used, using the `MutableList` class:

      from sqlalchemy import ARRAY
      from sqlalchemy.ext.mutable import MutableList

      class SomeOrmClass(Base):
          # ...

          data = Column(MutableList.as_mutable(ARRAY(Integer)))

  This extension will allow “in-place” changes such to the array such as `.append()` to produce events which will be detected by the unit of work. Note that changes to elements inside the array, including subarrays that are mutated in place, are not detected.

  Alternatively, assigning a new array value to an ORM element that replaces the old one will always trigger a change event.

  New in version 1.1.0.

  See also

  `sqlalchemy.dialects.postgresql.ARRAY`

  Members

  all(), any(), contains(), __init__(), comparator_factory, compare_values(), hashable, python_type, zero_indexes

  Class signature

  class `sqlalchemy.types.ARRAY` (`sqlalchemy.sql.expression.SchemaEventTarget`, `sqlalchemy.types.Indexable`, `sqlalchemy.types.Concatenable`, `sqlalchemy.types.TypeEngine`)

  class Comparator(expr)

    Define comparison operations for `ARRAY`.

    More operators are available on the dialect-specific form of this type. See `Comparator`.

    Class signature

    class `sqlalchemy.types.ARRAY.Comparator` (`sqlalchemy.types.Comparator`, `sqlalchemy.types.Comparator`)

    method `sqlalchemy.types.ARRAY.Comparator.`all(other, operator=None)

      Return `other operator ALL (array)` clause.

      Note

      This method is an `ARRAY` - specific construct that is now superseded by the `any_()` function, which features a different calling style. The `any_()` function is also mirrored at the method level via the `ColumnOperators.any_()` method.

      Usage of array-specific `Comparator.all()` is as follows:

          from sqlalchemy.sql import operators

          conn.execute(
              select(table.c.data).where(
                      table.c.data.all(7, operator=operators.lt)
                  )
          )

      Parameters:

        - other – expression to be compared

        - operator – an operator object from the `sqlalchemy.sql.operators` package, defaults to `eq()`.

      See also

      `all_()`

      `Comparator.any()`

    method `sqlalchemy.types.ARRAY.Comparator.`any(other, operator=None)

      Return `other operator ANY (array)` clause.

      Note

      This method is an `ARRAY` - specific construct that is now superseded by the `any_()` function, which features a different calling style. The `any_()` function is also mirrored at the method level via the `ColumnOperators.any_()` method.

      Usage of array-specific `Comparator.any()` is as follows:

          from sqlalchemy.sql import operators

          conn.execute(
              select(table.c.data).where(
                      table.c.data.any(7, operator=operators.lt)
                  )
          )

      Parameters:

        - other – expression to be compared

        - operator – an operator object from the `sqlalchemy.sql.operators` package, defaults to `eq()`.

      See also

      `any_()`

      `Comparator.all()`

    method `sqlalchemy.types.ARRAY.Comparator.`contains(*arg, **kw)

      Implement the ‘contains’ operator.

      Produces a LIKE expression that tests against a match for the middle of a string value:

          column LIKE '%' || <other> || '%'

      E.g.:

          stmt = select(sometable).\
              where(sometable.c.column.contains("foobar"))

      Since the operator uses `LIKE`, wildcard characters `"%"` and `"_"` that are present inside the <other> expression will behave like wildcards as well. For literal string values, the `ColumnOperators.contains.autoescape` flag may be set to `True` to apply escaping to occurrences of these characters within the string value so that they match as themselves and not as wildcard characters. Alternatively, the `ColumnOperators.contains.escape` parameter will establish a given character as an escape character which can be of use when the target expression is not a literal string.

      Parameters:

        - other – expression to be compared. This is usually a plain string value, but can also be an arbitrary SQL expression. LIKE wildcard characters `%` and `_` are not escaped by default unless the `ColumnOperators.contains.autoescape` flag is set to True.

        - autoescape –

          boolean; when True, establishes an escape character within the LIKE expression, then applies it to all occurrences of `"%"`, `"_"` and the escape character itself within the comparison value, which is assumed to be a literal string and not a SQL expression.

          An expression such as:

              somecolumn.contains("foo%bar", autoescape=True)

          Will render as:

              somecolumn LIKE '%' || :param || '%' ESCAPE '/'

          With the value of `:param` as `"foo/%bar"`.

        - escape –

          a character which when given will render with the `ESCAPE` keyword to establish that character as the escape character. This character can then be placed preceding occurrences of `%` and `_` to allow them to act as themselves and not wildcard characters.

          An expression such as:

              somecolumn.contains("foo/%bar", escape="^")

          Will render as:

              somecolumn LIKE '%' || :param || '%' ESCAPE '^'

          The parameter may also be combined with `ColumnOperators.contains.autoescape`:

              somecolumn.contains("foo%bar^bat", escape="^", autoescape=True)

          Where above, the given literal parameter will be converted to `"foo^%bar^^bat"` before being passed to the database.

      See also

      `ColumnOperators.startswith()`

      `ColumnOperators.endswith()`

      `ColumnOperators.like()`

  method `sqlalchemy.types.ARRAY.`__init__(item_type, as_tuple=False, dimensions=None, zero_indexes=False)

    Construct an `ARRAY`.

    E.g.:

        Column('myarray', ARRAY(Integer))

    Arguments are:

    Parameters:

      - item_type – The data type of items of this array. Note that dimensionality is irrelevant here, so multi-dimensional arrays like `INTEGER[][]`, are constructed as `ARRAY(Integer)`, not as `ARRAY(ARRAY(Integer))` or such.

      - as_tuple=False – Specify whether return results should be converted to tuples from lists. This parameter is not generally needed as a Python list corresponds well to a SQL array.

      - dimensions – if non-None, the ARRAY will assume a fixed number of dimensions. This impacts how the array is declared on the database, how it goes about interpreting Python and result values, as well as how expression behavior in conjunction with the “getitem” operator works. See the description at `ARRAY` for additional detail.

      - zero_indexes=False – when True, index values will be converted between Python zero-based and SQL one-based indexes, e.g. a value of one will be added to all index values before passing to the database.

  attribute `sqlalchemy.types.ARRAY.`comparator_factory

    alias of `Comparator`

  method `sqlalchemy.types.ARRAY.`compare_values(x, y)

    Compare two values for equality.

  attribute `sqlalchemy.types.ARRAY.`hashable

    Flag, if False, means values from this type aren’t hashable.

    Used by the ORM when uniquing result lists.

  attribute `sqlalchemy.types.ARRAY.`python_type
  attribute `sqlalchemy.types.ARRAY.`zero_indexes = False

    If True, Python zero-based indexes should be interpreted as one-based on the SQL expression side.

class sqlalchemy.types.BIGINT

  The SQL BIGINT type.

  Class signature

  class `sqlalchemy.types.BIGINT` (`sqlalchemy.types.BigInteger`)

class sqlalchemy.types.BINARY(length=None)

  The SQL BINARY type.

  Class signature

  class `sqlalchemy.types.BINARY` (`sqlalchemy.types._Binary`)

class sqlalchemy.types.BLOB(length=None)

  The SQL BLOB type.

  Class signature

  class `sqlalchemy.types.BLOB` (`sqlalchemy.types.LargeBinary`)

class sqlalchemy.types.BOOLEAN(create_constraint=False, name=None, _create_events=True)

  The SQL BOOLEAN type.

  Class signature

  class `sqlalchemy.types.BOOLEAN` (`sqlalchemy.types.Boolean`)

class sqlalchemy.types.CHAR(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  The SQL CHAR type.

  Class signature

  class `sqlalchemy.types.CHAR` (`sqlalchemy.types.String`)

class sqlalchemy.types.CLOB(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  The CLOB type.

  This type is found in Oracle and Informix.

  Class signature

  class `sqlalchemy.types.CLOB` (`sqlalchemy.types.Text`)

class sqlalchemy.types.DATE

  The SQL DATE type.

  Class signature

  class `sqlalchemy.types.DATE` (`sqlalchemy.types.Date`)

class sqlalchemy.types.DATETIME(timezone=False)

  The SQL DATETIME type.

  Class signature

  class `sqlalchemy.types.DATETIME` (`sqlalchemy.types.DateTime`)

class sqlalchemy.types.DECIMAL(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

  The SQL DECIMAL type.

  Class signature

  class `sqlalchemy.types.DECIMAL` (`sqlalchemy.types.Numeric`)

class sqlalchemy.types.FLOAT(precision=None, asdecimal=False, decimal_return_scale=None)

  The SQL FLOAT type.

  Class signature

  class `sqlalchemy.types.FLOAT` (`sqlalchemy.types.Float`)

attribute `sqlalchemy.types..`sqlalchemy.types.INT

  alias of `INTEGER`

class sqlalchemy.types.JSON(none_as_null=False)

  Represent a SQL JSON type.

  Note

  `JSON` is provided as a facade for vendor-specific JSON types. Since it supports JSON SQL operations, it only works on backends that have an actual JSON type, currently:

  - PostgreSQL - see `sqlalchemy.dialects.postgresql.JSON` and `sqlalchemy.dialects.postgresql.JSONB` for backend-specific notes

  - MySQL - see `sqlalchemy.dialects.mysql.JSON` for backend-specific notes

  - SQLite as of version 3.9 - see `sqlalchemy.dialects.sqlite.JSON` for backend-specific notes

  - Microsoft SQL Server 2016 and later - see `sqlalchemy.dialects.mssql.JSON` for backend-specific notes

  `JSON` is part of the Core in support of the growing popularity of native JSON datatypes.

  The `JSON` type stores arbitrary JSON format data, e.g.:

      data_table = Table('data_table', metadata,
          Column('id', Integer, primary_key=True),
          Column('data', JSON)
      )

      with engine.connect() as conn:
          conn.execute(
              data_table.insert(),
              {"data": {"key1": "value1", "key2": "value2"}}
          )

  JSON-Specific Expression Operators

  The `JSON` datatype provides these additional SQL operations:

  - Keyed index operations:

        data_table.c.data['some key']

  - Integer index operations:

        data_table.c.data[3]

  - Path index operations:

        data_table.c.data[('key_1', 'key_2', 5, ..., 'key_n')]

  - Data casters for specific JSON element types, subsequent to an index or path operation being invoked:

        data_table.c.data["some key"].as_integer()

    New in version 1.3.11.

  Additional operations may be available from the dialect-specific versions of `JSON`, such as `sqlalchemy.dialects.postgresql.JSON` and `sqlalchemy.dialects.postgresql.JSONB` which both offer additional PostgreSQL-specific operations.

  Casting JSON Elements to Other Types

  Index operations, i.e. those invoked by calling upon the expression using the Python bracket operator as in `some_column['some key']`, return an expression object whose type defaults to `JSON` by default, so that further JSON-oriented instructions may be called upon the result type. However, it is likely more common that an index operation is expected to return a specific scalar element, such as a string or integer. In order to provide access to these elements in a backend-agnostic way, a series of data casters are provided:

  - `Comparator.as_string()` - return the element as a string

  - `Comparator.as_boolean()` - return the element as a boolean

  - `Comparator.as_float()` - return the element as a float

  - `Comparator.as_integer()` - return the element as an integer

  These data casters are implemented by supporting dialects in order to assure that comparisons to the above types will work as expected, such as:

      # integer comparison
      data_table.c.data["some_integer_key"].as_integer() == 5

      # boolean comparison
      data_table.c.data["some_boolean"].as_boolean() == True

  New in version 1.3.11: Added type-specific casters for the basic JSON data element types.

  Note

  The data caster functions are new in version 1.3.11, and supersede the previous documented approaches of using CAST; for reference, this looked like:

      from sqlalchemy import cast, type_coerce
      from sqlalchemy import String, JSON
      cast(
          data_table.c.data['some_key'], String
      ) == type_coerce(55, JSON)

  The above case now works directly as:

      data_table.c.data['some_key'].as_integer() == 5

  For details on the previous comparison approach within the 1.3.x series, see the documentation for SQLAlchemy 1.2 or the included HTML files in the doc/ directory of the version’s distribution.

  Detecting Changes in JSON columns when using the ORM

  The `JSON` type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the structure. In order to detect these, the `sqlalchemy.ext.mutable` extension must be used, most typically using the `MutableDict` class. This extension will allow “in-place” changes to the datastructure to produce events which will be detected by the unit of work. See the example at `HSTORE` for a simple example involving a dictionary.

  Alternatively, assigning a JSON structure to an ORM element that replaces the old one will always trigger a change event.

  Support for JSON null vs. SQL NULL

  When working with NULL values, the `JSON` type recommends the use of two specific constants in order to differentiate between a column that evaluates to SQL NULL, e.g. no value, vs. the JSON-encoded string of `"null"`. To insert or select against a value that is SQL NULL, use the constant `null()`. This symbol may be passed as a parameter value specifically when using the `JSON` datatype, which contains special logic that interprets this symbol to mean that the column value should be SQL NULL as opposed to JSON `"null"`:

      from sqlalchemy import null
      conn.execute(table.insert(), {"json_value": null()})

  To insert or select against a value that is JSON `"null"`, use the constant `JSON.NULL`:

      conn.execute(table.insert(), {"json_value": JSON.NULL})

  The `JSON` type supports a flag `JSON.none_as_null` which when set to True will result in the Python constant `None` evaluating to the value of SQL NULL, and when set to False results in the Python constant `None` evaluating to the value of JSON `"null"`. The Python value `None` may be used in conjunction with either `JSON.NULL` and `null()` in order to indicate NULL values, but care must be taken as to the value of the `JSON.none_as_null` in these cases.

  Customizing the JSON Serializer

  The JSON serializer and deserializer used by `JSON` defaults to Python’s `json.dumps` and `json.loads` functions; in the case of the psycopg2 dialect, psycopg2 may be using its own custom loader function.

  In order to affect the serializer / deserializer, they are currently configurable at the `create_engine()` level via the `create_engine.json_serializer` and `create_engine.json_deserializer` parameters. For example, to turn off `ensure_ascii`:

      engine = create_engine(
          "sqlite://",
          json_serializer=lambda obj: json.dumps(obj, ensure_ascii=False))

  Changed in version 1.3.7: SQLite dialect’s `json_serializer` and `json_deserializer` parameters renamed from `_json_serializer` and `_json_deserializer`.

  See also

  `sqlalchemy.dialects.postgresql.JSON`

  `sqlalchemy.dialects.postgresql.JSONB`

  `sqlalchemy.dialects.mysql.JSON`

  `sqlalchemy.dialects.sqlite.JSON`

  New in version 1.1.

  Members

  as_boolean(), as_float(), as_integer(), as_json(), as_numeric(), as_string(), bind_processor(), literal_processor(), NULL, __init__(), bind_processor(), comparator_factory, hashable, python_type, result_processor(), should_evaluate_none

  Class signature

  class `sqlalchemy.types.JSON` (`sqlalchemy.types.Indexable`, `sqlalchemy.types.TypeEngine`)

  class Comparator(expr)

    Define comparison operations for `JSON`.

    Class signature

    class `sqlalchemy.types.JSON.Comparator` (`sqlalchemy.types.Comparator`, `sqlalchemy.types.Comparator`)

    method `sqlalchemy.types.JSON.Comparator.`as_boolean()

      Cast an indexed value as boolean.

      e.g.:

          stmt = select(
              mytable.c.json_column['some_data'].as_boolean()
          ).where(
              mytable.c.json_column['some_data'].as_boolean() == True
          )

      New in version 1.3.11.

    method `sqlalchemy.types.JSON.Comparator.`as_float()

      Cast an indexed value as float.

      e.g.:

          stmt = select(
              mytable.c.json_column['some_data'].as_float()
          ).where(
              mytable.c.json_column['some_data'].as_float() == 29.75
          )

      New in version 1.3.11.

    method `sqlalchemy.types.JSON.Comparator.`as_integer()

      Cast an indexed value as integer.

      e.g.:

          stmt = select(
              mytable.c.json_column['some_data'].as_integer()
          ).where(
              mytable.c.json_column['some_data'].as_integer() == 5
          )

      New in version 1.3.11.

    method `sqlalchemy.types.JSON.Comparator.`as_json()

      Cast an indexed value as JSON.

      e.g.:

          stmt = select(mytable.c.json_column['some_data'].as_json())

      This is typically the default behavior of indexed elements in any case.

      Note that comparison of full JSON structures may not be supported by all backends.

      New in version 1.3.11.

    method `sqlalchemy.types.JSON.Comparator.`as_numeric(precision, scale, asdecimal=True)

      Cast an indexed value as numeric/decimal.

      e.g.:

          stmt = select(
              mytable.c.json_column['some_data'].as_numeric(10, 6)
          ).where(
              mytable.c.
              json_column['some_data'].as_numeric(10, 6) == 29.75
          )

      New in version 1.4.0b2.

    method `sqlalchemy.types.JSON.Comparator.`as_string()

      Cast an indexed value as string.

      e.g.:

          stmt = select(
              mytable.c.json_column['some_data'].as_string()
          ).where(
              mytable.c.json_column['some_data'].as_string() ==
              'some string'
          )

      New in version 1.3.11.

  class JSONElementType

    Common function for index / path elements in a JSON expression.

    Class signature

    class `sqlalchemy.types.JSON.JSONElementType` (`sqlalchemy.types.TypeEngine`)

    method `sqlalchemy.types.JSON.JSONElementType.`bind_processor(dialect)

      Return a conversion function for processing bind values.

      Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

      If processing is not necessary, the method should return `None`.

      Note

      This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

      To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

      See also

      Augmenting Existing Types

      Parameters:

        dialect – Dialect instance in use.

    method `sqlalchemy.types.JSON.JSONElementType.`literal_processor(dialect)

      Return a conversion function for processing literal values that are to be rendered directly without using binds.

      This function is used when the compiler makes use of the “literal_binds” flag, typically used in DDL generation as well as in certain scenarios where backends don’t accept bound parameters.

      Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

      Note

      This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.literal_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

      To provide alternate behavior for `TypeEngine.literal_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_literal_param()`.

      See also

      Augmenting Existing Types

  class JSONIndexType

    Placeholder for the datatype of a JSON index value.

    This allows execution-time processing of JSON index values for special syntaxes.

    Class signature

    class `sqlalchemy.types.JSON.JSONIndexType` (`sqlalchemy.types.JSONElementType`)

  class JSONIntIndexType

    Placeholder for the datatype of a JSON index value.

    This allows execution-time processing of JSON index values for special syntaxes.

    Class signature

    class `sqlalchemy.types.JSON.JSONIntIndexType` (`sqlalchemy.types.JSONIndexType`)

  class JSONPathType

    Placeholder type for JSON path operations.

    This allows execution-time processing of a path-based index value into a specific SQL syntax.

    Class signature

    class `sqlalchemy.types.JSON.JSONPathType` (`sqlalchemy.types.JSONElementType`)

  class JSONStrIndexType

    Placeholder for the datatype of a JSON index value.

    This allows execution-time processing of JSON index values for special syntaxes.

    Class signature

    class `sqlalchemy.types.JSON.JSONStrIndexType` (`sqlalchemy.types.JSONIndexType`)

  attribute `sqlalchemy.types.JSON.`NULL = symbol('JSON_NULL')

    Describe the json value of NULL.

    This value is used to force the JSON value of `"null"` to be used as the value. A value of Python `None` will be recognized either as SQL NULL or JSON `"null"`, based on the setting of the `JSON.none_as_null` flag; the `JSON.NULL` constant can be used to always resolve to JSON `"null"` regardless of this setting. This is in contrast to the `null()` construct, which always resolves to SQL NULL. E.g.:

        from sqlalchemy import null
        from sqlalchemy.dialects.postgresql import JSON

        # will *always* insert SQL NULL
        obj1 = MyObject(json_value=null())

        # will *always* insert JSON string "null"
        obj2 = MyObject(json_value=JSON.NULL)

        session.add_all([obj1, obj2])
        session.commit()

    In order to set JSON NULL as a default value for a column, the most transparent method is to use `text()`:

        Table(
            'my_table', metadata,
            Column('json_data', JSON, default=text("'null'"))
        )

    While it is possible to use `JSON.NULL` in this context, the `JSON.NULL` value will be returned as the value of the column, which in the context of the ORM or other repurposing of the default value, may not be desirable. Using a SQL expression means the value will be re-fetched from the database within the context of retrieving generated defaults.

  method `sqlalchemy.types.JSON.`__init__(none_as_null=False)

    Construct a `JSON` type.

    Parameters:

      none_as_null=False –

      if True, persist the value `None` as a SQL NULL value, not the JSON encoding of `null`. Note that when this flag is False, the `null()` construct can still be used to persist a NULL value, which may be passed directly as a parameter value that is specially interpreted by the `JSON` type as SQL NULL:

          from sqlalchemy import null
          conn.execute(table.insert(), {"data": null()})

      Note

      `JSON.none_as_null` does not apply to the values passed to `Column.default` and `Column.server_default`; a value of `None` passed for these parameters means “no default present”.

      Additionally, when used in SQL comparison expressions, the Python value `None` continues to refer to SQL null, and not JSON NULL. The `JSON.none_as_null` flag refers explicitly to the persistence of the value within an INSERT or UPDATE statement. The `JSON.NULL` value should be used for SQL expressions that wish to compare to JSON null.

      See also

      `JSON.NULL`

  method `sqlalchemy.types.JSON.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  attribute `sqlalchemy.types.JSON.`comparator_factory

    alias of `Comparator`

  attribute `sqlalchemy.types.JSON.`hashable = False

    Flag, if False, means values from this type aren’t hashable.

    Used by the ORM when uniquing result lists.

  attribute `sqlalchemy.types.JSON.`python_type
  method `sqlalchemy.types.JSON.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Note

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

  attribute `sqlalchemy.types.JSON.`should_evaluate_none

    If True, the Python constant `None` is considered to be handled explicitly by this type.

    The ORM uses this flag to indicate that a positive value of `None` is passed to the column in an INSERT statement, rather than omitting the column from the INSERT statement which has the effect of firing off column-level defaults. It also allows types which have special behavior for Python None, such as a JSON type, to indicate that they’d like to handle the None value explicitly.

    To set this flag on an existing type, use the `TypeEngine.evaluates_none()` method.

    See also

    `TypeEngine.evaluates_none()`

    New in version 1.1.

class sqlalchemy.types.INTEGER

  The SQL INT or INTEGER type.

  Class signature

  class `sqlalchemy.types.INTEGER` (`sqlalchemy.types.Integer`)

class sqlalchemy.types.NCHAR(length=None, **kwargs)

  The SQL NCHAR type.

  Class signature

  class `sqlalchemy.types.NCHAR` (`sqlalchemy.types.Unicode`)

class sqlalchemy.types.NVARCHAR(length=None, **kwargs)

  The SQL NVARCHAR type.

  Class signature

  class `sqlalchemy.types.NVARCHAR` (`sqlalchemy.types.Unicode`)

class sqlalchemy.types.NUMERIC(precision=None, scale=None, decimal_return_scale=None, asdecimal=True)

  The SQL NUMERIC type.

  Class signature

  class `sqlalchemy.types.NUMERIC` (`sqlalchemy.types.Numeric`)

class sqlalchemy.types.REAL(precision=None, asdecimal=False, decimal_return_scale=None)

  The SQL REAL type.

  Class signature

  class `sqlalchemy.types.REAL` (`sqlalchemy.types.Float`)

class sqlalchemy.types.SMALLINT

  The SQL SMALLINT type.

  Class signature

  class `sqlalchemy.types.SMALLINT` (`sqlalchemy.types.SmallInteger`)

class sqlalchemy.types.TEXT(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  The SQL TEXT type.

  Class signature

  class `sqlalchemy.types.TEXT` (`sqlalchemy.types.Text`)

class sqlalchemy.types.TIME(timezone=False)

  The SQL TIME type.

  Class signature

  class `sqlalchemy.types.TIME` (`sqlalchemy.types.Time`)

class sqlalchemy.types.TIMESTAMP(timezone=False)

  The SQL TIMESTAMP type.

  `TIMESTAMP` datatypes have support for timezone storage on some backends, such as PostgreSQL and Oracle. Use the `TIMESTAMP.timezone` argument in order to enable “TIMESTAMP WITH TIMEZONE” for these backends.

  Members

  __init__(), get_dbapi_type()

  Class signature

  class `sqlalchemy.types.TIMESTAMP` (`sqlalchemy.types.DateTime`)

  method `sqlalchemy.types.TIMESTAMP.`__init__(timezone=False)

    Construct a new `TIMESTAMP`.

    Parameters:

      timezone – boolean. Indicates that the TIMESTAMP type should enable timezone support, if available on the target database. On a per-dialect basis is similar to “TIMESTAMP WITH TIMEZONE”. If the target database does not support timezones, this flag is ignored.

  method `sqlalchemy.types.TIMESTAMP.`get_dbapi_type(dbapi)

    Return the corresponding type object from the underlying DB-API, if any.

    This can be useful for calling `setinputsizes()`, for example.

class sqlalchemy.types.VARBINARY(length=None)

  The SQL VARBINARY type.

  Class signature

  class `sqlalchemy.types.VARBINARY` (`sqlalchemy.types._Binary`)

class sqlalchemy.types.VARCHAR(length=None, collation=None, convert_unicode=False, unicode_error=None, _warn_on_bytestring=False, _expect_unicode=False)

  The SQL VARCHAR type.

  Class signature

  class `sqlalchemy.types.VARCHAR` (`sqlalchemy.types.String`)