# Class JdbcPkGenerator

java.lang.Object
org.apache.cayenne.dba.JdbcPkGenerator

All Implemented Interfaces:
  `PkGenerator`

Direct Known Subclasses:
  `FrontBasePkGenerator, MySQLPkGenerator, SequencePkGenerator, SQLServerPkGenerator, SybasePkGenerator`

public class JdbcPkGenerator extends Object implements PkGenerator
Default primary key generator implementation. Uses a lookup table named "AUTO_PK_SUPPORT" to search and increment primary keys for tables.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected final JdbcAdapter`
  `adapter`
  `static final int`
  `DEFAULT_PK_CACHE_SIZE`
  `protected ConcurrentMap<String, Queue<Long>>`
  `pkCache`
  `protected int`
  `pkCacheSize`
  `protected long`
  `pkStartValue`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `JdbcPkGenerator(JdbcAdapter adapter)`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected boolean`
  `autoPkTableExists(DataNode node)`
  Checks if AUTO_PK_TABLE already exists in the database.
  `void`
  `createAutoPk(DataNode node, List<DbEntity> dbEntities)`
  Generates necessary database objects to provide automatic primary key support.
  `List<String>`
  `createAutoPkStatements(List<DbEntity> dbEntities)`
  Returns a list of SQL strings needed to generates database objects to provide automatic primary support for the list of entities.
  `void`
  `dropAutoPk(DataNode node, List<DbEntity> dbEntities)`
  Drops table named "AUTO_PK_SUPPORT" if it exists in the database.
  `List<String>`
  `dropAutoPkStatements(List<DbEntity> dbEntities)`
  Returns SQL string needed to drop database objects associated with automatic primary key generation.
  `protected String`
  `dropAutoPkString()`
  `Object`
  `generatePk(DataNode node, DbAttribute pk, Class<?> javaType)`
  Generates a unique and non-repeating primary key for the specified PK attribute
  `JdbcAdapter`
  `getAdapter()`
  Get an adapter associated with current PkGenerator
  `int`
  `getPkCacheSize()`
  Returns a size of the entity primary key cache.
  `protected long`
  `longPkFromDatabase(DataNode node, DbEntity entity)`
  Performs primary key generation ignoring cache.
  `protected String`
  `pkCreateString(String entName)`
  `protected String`
  `pkDeleteString(List<DbEntity> dbEntities)`
  `protected String`
  `pkSelectString(String entName)`
  `protected String`
  `pkTableCreateString()`
  `protected String`
  `pkUpdateString(String entName)`
  `void`
  `reset()`
  Resets any cached primary keys forcing generator to go to the database next time id generation is requested.
  `int`
  `runUpdate(DataNode node, String sql)`
  Runs JDBC update over a Connection obtained from DataNode.
  `void`
  `setPkCacheSize(int pkCacheSize)`
  Sets the size of the entity primary key cache.

  ### Methods inherited from class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

  ### Methods inherited from interface PkGenerator

  `generatePk`

- ## Field Details

  - ### DEFAULT_PK_CACHE_SIZE

    public static final int DEFAULT_PK_CACHE_SIZE
    See Also:
      - Constant Field Values

  - ### adapter

    protected final JdbcAdapter adapter

  - ### pkCache

    protected ConcurrentMap<String, Queue<Long>> pkCache

  - ### pkCacheSize

    protected int pkCacheSize

  - ### pkStartValue

    protected long pkStartValue

- ## Constructor Details

  - ### JdbcPkGenerator

    public JdbcPkGenerator(JdbcAdapter adapter)

- ## Method Details

  - ### getAdapter

    public JdbcAdapter getAdapter()
    Description copied from interface: `PkGenerator`
    Get an adapter associated with current PkGenerator
    Specified by:
      `getAdapter` in interface `PkGenerator`

  - ### createAutoPk

    public void createAutoPk(DataNode node, List<DbEntity> dbEntities)
    Description copied from interface: `PkGenerator`
    Generates necessary database objects to provide automatic primary key support.
    Specified by:
      `createAutoPk` in interface `PkGenerator`
    Parameters:
      `node` - node that provides access to a DataSource.
      `dbEntities` - a list of entities that require primary key auto-generation support

  - ### createAutoPkStatements

    public List<String> createAutoPkStatements(List<DbEntity> dbEntities)
    Description copied from interface: `PkGenerator`
    Returns a list of SQL strings needed to generates database objects to provide automatic primary support for the list of entities. No actual database operations are performed.
    Specified by:
      `createAutoPkStatements` in interface `PkGenerator`

  - ### dropAutoPk

    public void dropAutoPk(DataNode node, List<DbEntity> dbEntities)
    Drops table named "AUTO_PK_SUPPORT" if it exists in the database.
    Specified by:
      `dropAutoPk` in interface `PkGenerator`
    Parameters:
      `node` - node that provides access to a DataSource.
      `dbEntities` - a list of entities whose primary key auto-generation support should be dropped.

  - ### dropAutoPkStatements

    public List<String> dropAutoPkStatements(List<DbEntity> dbEntities)
    Description copied from interface: `PkGenerator`
    Returns SQL string needed to drop database objects associated with automatic primary key generation. No actual database operations are performed.
    Specified by:
      `dropAutoPkStatements` in interface `PkGenerator`

  - ### pkTableCreateString

    protected String pkTableCreateString()

  - ### pkDeleteString

    protected String pkDeleteString(List<DbEntity> dbEntities)

  - ### pkCreateString

    protected String pkCreateString(String entName)

  - ### pkSelectString

    protected String pkSelectString(String entName)

  - ### pkUpdateString

    protected String pkUpdateString(String entName)

  - ### dropAutoPkString

    protected String dropAutoPkString()

  - ### autoPkTableExists

    protected boolean autoPkTableExists(DataNode node)
    Checks if AUTO_PK_TABLE already exists in the database.

  - ### runUpdate

    public int runUpdate(DataNode node, String sql)
    Runs JDBC update over a Connection obtained from DataNode. Returns a number of objects returned from update.

  - ### generatePk

    public Object generatePk(DataNode node, DbAttribute pk, Class<?> javaType)
    Description copied from interface: `PkGenerator`
    Generates a unique and non-repeating primary key for the specified PK attribute
    Specified by:
      `generatePk` in interface `PkGenerator`

  - ### longPkFromDatabase

    protected long longPkFromDatabase(DataNode node, DbEntity entity)
    Performs primary key generation ignoring cache. Generates a range of primary keys as specified by "pkCacheSize" bean property.

    This method is called internally from "generatePkForDbEntity" and then generated range of key values is saved in cache for performance. Subclasses that implement different primary key generation solutions should override this method, not "generatePkForDbEntity".

    Since:
      3.0

  - ### getPkCacheSize

    public int getPkCacheSize()
    Returns a size of the entity primary key cache. Default value is 20. If cache size is set to a value less or equals than "one", no primary key caching is done.

  - ### setPkCacheSize

    public void setPkCacheSize(int pkCacheSize)
    Sets the size of the entity primary key cache. If `pkCacheSize` parameter is less than 1, cache size is set to "one".

    Note that our tests show that setting primary key cache value to anything much bigger than 20 does not give any significant performance increase. Therefore it does not make sense to use bigger values, since this may potentially create big gaps in the database primary key sequences in cases like application crashes or restarts.

  - ### reset

    public void reset()
    Description copied from interface: `PkGenerator`
    Resets any cached primary keys forcing generator to go to the database next time id generation is requested. May not be applicable for all generator implementations.
    Specified by:
      `reset` in interface `PkGenerator`