ForeignKeyNullifier (Oracle - Berkeley DB Java API)
Date: 2013-09-09

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## com.sleepycat.db
Interface ForeignKeyNullifier

All Known Implementing Classes:
  SerialSerialKeyCreator, TupleSerialKeyCreator, TupleSerialMarshalledKeyCreator, TupleTupleKeyCreator, TupleTupleMarshalledKeyCreator

    public interface ForeignKeyNullifier

The interface implemented for setting single-valued foreign keys to null.

A key nullifier is used with a secondary database that is configured to have a foreign key integrity constraint and a delete action of `ForeignKeyDeleteAction.NULLIFY`. The key nullifier is specified by calling `SecondaryConfig.setForeignKeyNullifier(com.sleepycat.db.ForeignKeyNullifier)`.

When a referenced record in the foreign key database is deleted and the foreign key delete action is `NULLIFY`, the `nullifyForeignKey(com.sleepycat.db.SecondaryDatabase, com.sleepycat.db.DatabaseEntry)` method is called. This method sets the foreign key reference to null in the datum of the primary database. The primary database is then updated to contain the modified datum. The result is that the secondary key is deleted.

This interface may be used along with `SecondaryKeyCreator` for many-to-one and one-to-one relationships. It may not be used with `SecondaryMultiKeyCreator` because the secondary key is not passed as a parameter to the nullifyForeignKey method and this method would not know which key to nullify. When using `SecondaryMultiKeyCreator`, use `ForeignMultiKeyNullifier` instead.

Method Summary
`boolean` | `nullifyForeignKey(SecondaryDatabase secondary, DatabaseEntry data)` Sets the foreign key reference to null in the datum of the primary database.

Method Detail

### nullifyForeignKey

    boolean nullifyForeignKey(SecondaryDatabase secondary,
                              DatabaseEntry data)
                              throws DatabaseException

  Sets the foreign key reference to null in the datum of the primary database.

  Parameters:
    `secondary` - the database in which the foreign key integrity constraint is defined. This parameter is passed for informational purposes but is not commonly used.
    `data` - the existing primary datum in which the foreign key reference should be set to null. This parameter should be updated by this method if it returns true.
  Returns:
    true if the datum was modified, or false to indicate that the key is not present.
  Throws:
    `DatabaseException` - if an error occurs attempting to clear the key reference.

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