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## weka.core.converters
Class DatabaseLoader

    java.lang.Object
      weka.core.converters.AbstractLoader
          weka.core.converters.DatabaseLoader

All Implemented Interfaces:
  java.io.Serializable, BatchConverter, DatabaseConverter, IncrementalConverter, Loader, OptionHandler, RevisionHandler

    public class DatabaseLoader

extends AbstractLoader
implements BatchConverter, IncrementalConverter, DatabaseConverter, OptionHandler

Reads Instances from a Database. Can read a database in batch or incremental mode.
In inremental mode MySQL and HSQLDB are supported.
For all other DBMS set a pseudoincremental mode is used:
In pseudo incremental mode the instances are read into main memory all at once and then incrementally provided to the user.
For incremental loading the rows in the database table have to be ordered uniquely.
The reason for this is that every time only a single row is fetched by extending the user query by a LIMIT clause.
If this extension is impossible instances will be loaded pseudoincrementally. To ensure that every row is fetched exaclty once, they have to ordered.
Therefore a (primary) key is necessary.This approach is chosen, instead of using JDBC driver facilities, because the latter one differ betweeen different drivers.
If you use the DatabaseSaver and save instances by generating automatically a primary key (its name is defined in DtabaseUtils), this primary key will be used for ordering but will not be part of the output. The user defined SQL query to extract the instances should not contain LIMIT and ORDER BY clauses (see -Q option).
In addition, for incremental loading, you can define in the DatabaseUtils file how many distinct values a nominal attribute is allowed to have. If this number is exceeded, the column will become a string attribute.
In batch mode no string attributes will be created.

Valid options are:

     -url <JDBC URL>
      The JDBC URL to connect to.
      (default: from DatabaseUtils.props file)

     -user <name>
      The user to connect with to the database.
      (default: none)

     -password <password>
      The password to connect with to the database.
      (default: none)

     -Q <query>
      SQL query of the form
       SELECT <list of columns>|* FROM <table> [WHERE]
      to execute.
      (default: Select * From Results0)

     -P <list of column names>
      List of column names uniquely defining a DB row
      (separated by ', ').
      Used for incremental loading.
      If not specified, the key will be determined automatically,
      if possible with the used JDBC driver.
      The auto ID column created by the DatabaseSaver won't be loaded.

     -I
      Sets incremental loading

Version:
  $Revision: 6332 $
Author:
  Stefan Mutter (mutter@cs.waikato.ac.nz)
See Also:
  `Loader`, Serialized Form

Constructor Summary
`DatabaseLoader()` Constructor

Method Summary
`void` | `connectToDatabase()` Opens a connection to the database
`Instances` | `getDataSet()` Return the full data set in batch mode (header and all intances at once).
`java.lang.String` | `getKeys()` Gets the key columns' name
`Instance` | `getNextInstance(Instances structure)` Read the data set incrementally---get the next instance in the data set or returns null if there are no more instances to get.
`java.lang.String[]` | `getOptions()` Gets the setting
`java.lang.String` | `getPassword()` Returns the database password
`java.lang.String` | `getQuery()` Gets the query to execute against the database
`java.lang.String` | `getRevision()` Returns the revision string.
`Instances` | `getStructure()` Determines and returns (if possible) the structure (internally the header) of the data set as an empty set of instances.
`java.lang.String` | `getUrl()` Gets the URL
`java.lang.String` | `getUser()` Gets the user name
`java.lang.String` | `globalInfo()` Returns a string describing this Loader
`java.lang.String` | `keysTipText()` the tip text for this property
`java.util.Enumeration` | `listOptions()` Lists the available options
`static void` | `main(java.lang.String[] options)` Main method.
`java.lang.String` | `passwordTipText()` the tip text for this property
`java.lang.String` | `queryTipText()` the tip text for this property
`void` | `reset()` Resets the Loader ready to read a new data set
`void` | `resetStructure()` Resets the structure of instances
`void` | `setKeys(java.lang.String keys)` Sets the key columns of a database table
`void` | `setOptions(java.lang.String[] options)` Sets the options.
`void` | `setPassword(java.lang.String password)` Sets user password for the database
`void` | `setQuery(java.lang.String q)` Sets the query to execute against the database
`void` | `setSource()` Sets the database url using the DatabaseUtils file
`void` | `setSource(java.lang.String url)` Sets the database url
`void` | `setSource(java.lang.String url, java.lang.String userName, java.lang.String password)` Sets the database url, user and pw
`void` | `setUrl(java.lang.String url)` Sets the database URL
`void` | `setUser(java.lang.String user)` Sets the database user
`java.lang.String` | `urlTipText()` the tip text for this property
`java.lang.String` | `userTipText()` the tip text for this property

Methods inherited from class weka.core.converters.AbstractLoader
`setSource, setSource`

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### DatabaseLoader

    public DatabaseLoader()
                   throws java.lang.Exception

  Constructor

  Throws:
    `java.lang.Exception` - if initialization fails

Method Detail

### globalInfo

    public java.lang.String globalInfo()

  Returns a string describing this Loader

  Returns:
    a description of the Loader suitable for displaying in the explorer/experimenter gui

### reset

    public void reset()
               throws java.lang.Exception

  Resets the Loader ready to read a new data set

  Specified by:
    `reset` in interface `Loader`
  Overrides:
    `reset` in class `AbstractLoader`
  Throws:
    `java.lang.Exception` - if an error occurs while disconnecting from the database

### resetStructure

    public void resetStructure()

  Resets the structure of instances

### setQuery

    public void setQuery(java.lang.String q)

  Sets the query to execute against the database

  Parameters:
    `q` - the query to execute

### getQuery

    public java.lang.String getQuery()

  Gets the query to execute against the database

  Returns:
    the query

### queryTipText

    public java.lang.String queryTipText()

  the tip text for this property

  Returns:
    the tip text

### setKeys

    public void setKeys(java.lang.String keys)

  Sets the key columns of a database table

  Parameters:
    `keys` - a String containing the key columns in a comma separated list.

### getKeys

    public java.lang.String getKeys()

  Gets the key columns' name

  Returns:
    name of the key columns'

### keysTipText

    public java.lang.String keysTipText()

  the tip text for this property

  Returns:
    the tip text

### setUrl

    public void setUrl(java.lang.String url)

  Sets the database URL

  Specified by:
    `setUrl` in interface `DatabaseConverter`
  Parameters:
    `url` - string with the database URL

### getUrl

    public java.lang.String getUrl()

  Gets the URL

  Specified by:
    `getUrl` in interface `DatabaseConverter`
  Returns:
    the URL

### urlTipText

    public java.lang.String urlTipText()

  the tip text for this property

  Returns:
    the tip text

### setUser

    public void setUser(java.lang.String user)

  Sets the database user

  Specified by:
    `setUser` in interface `DatabaseConverter`
  Parameters:
    `user` - the database user name

### getUser

    public java.lang.String getUser()

  Gets the user name

  Specified by:
    `getUser` in interface `DatabaseConverter`
  Returns:
    name of database user

### userTipText

    public java.lang.String userTipText()

  the tip text for this property

  Returns:
    the tip text

### setPassword

    public void setPassword(java.lang.String password)

  Sets user password for the database

  Specified by:
    `setPassword` in interface `DatabaseConverter`
  Parameters:
    `password` - the password

### getPassword

    public java.lang.String getPassword()

  Returns the database password

  Returns:
    the database password

### passwordTipText

    public java.lang.String passwordTipText()

  the tip text for this property

  Returns:
    the tip text

### setSource

    public void setSource(java.lang.String url,
                          java.lang.String userName,
                          java.lang.String password)

  Sets the database url, user and pw

  Parameters:
    `url` - the database url
    `userName` - the user name
    `password` - the password

### setSource

    public void setSource(java.lang.String url)

  Sets the database url

  Parameters:
    `url` - the database url

### setSource

    public void setSource()
                   throws java.lang.Exception

  Sets the database url using the DatabaseUtils file

  Throws:
    `java.lang.Exception` - if something goes wrong

### connectToDatabase

    public void connectToDatabase()

  Opens a connection to the database

### getStructure

    public Instances getStructure()
                           throws java.io.IOException

  Determines and returns (if possible) the structure (internally the header) of the data set as an empty set of instances.

  Specified by:
    `getStructure` in interface `Loader`
  Specified by:
    `getStructure` in class `AbstractLoader`
  Returns:
    the structure of the data set as an empty set of Instances
  Throws:
    `java.io.IOException` - if an error occurs

### getDataSet

    public Instances getDataSet()
                         throws java.io.IOException

  Return the full data set in batch mode (header and all intances at once).

  Specified by:
    `getDataSet` in interface `Loader`
  Specified by:
    `getDataSet` in class `AbstractLoader`
  Returns:
    the structure of the data set as an empty set of Instances
  Throws:
    `java.io.IOException` - if there is no source or parsing fails

### getNextInstance

    public Instance getNextInstance(Instances structure)
                             throws java.io.IOException

  Read the data set incrementally---get the next instance in the data set or returns null if there are no more instances to get. If the structure hasn't yet been determined by a call to getStructure then method does so before returning the next instance in the data set.

  Specified by:
    `getNextInstance` in interface `Loader`
  Specified by:
    `getNextInstance` in class `AbstractLoader`
  Parameters:
    `structure` - the dataset header information, will get updated in case of string or relational attributes
  Returns:
    the next instance in the data set as an Instance object or null if there are no more instances to be read
  Throws:
    `java.io.IOException` - if there is an error during parsing

### getOptions

    public java.lang.String[] getOptions()

  Gets the setting

  Specified by:
    `getOptions` in interface `OptionHandler`
  Returns:
    the current setting

### listOptions

    public java.util.Enumeration listOptions()

  Lists the available options

  Specified by:
    `listOptions` in interface `OptionHandler`
  Returns:
    an enumeration of the available options

### setOptions

    public void setOptions(java.lang.String[] options)
                    throws java.lang.Exception

  Sets the options. Valid options are:

       -url <JDBC URL>
        The JDBC URL to connect to.
        (default: from DatabaseUtils.props file)

       -user <name>
        The user to connect with to the database.
        (default: none)

       -password <password>
        The password to connect with to the database.
        (default: none)

       -Q <query>
        SQL query of the form
         SELECT <list of columns>|* FROM <table> [WHERE]
        to execute.
        (default: Select * From Results0)

       -P <list of column names>
        List of column names uniquely defining a DB row
        (separated by ', ').
        Used for incremental loading.
        If not specified, the key will be determined automatically,
        if possible with the used JDBC driver.
        The auto ID column created by the DatabaseSaver won't be loaded.

       -I
        Sets incremental loading

  Specified by:
    `setOptions` in interface `OptionHandler`
  Parameters:
    `options` - the options
  Throws:
    `java.lang.Exception` - if options cannot be set

### getRevision

    public java.lang.String getRevision()

  Returns the revision string.

  Specified by:
    `getRevision` in interface `RevisionHandler`
  Returns:
    the revision

### main

    public static void main(java.lang.String[] options)

  Main method.

  Parameters:
    `options` - the options

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