ForeignMultiKeyNullifier (Oracle - Berkeley DB Java API)
Date: 2017-04-13

com.sleepycat.db

## Interface ForeignMultiKeyNullifier

-     public interface ForeignMultiKeyNullifier

  The interface implemented for setting multi-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.setForeignMultiKeyNullifier(com.sleepycat.db.ForeignMultiKeyNullifier)`.

  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, com.sleepycat.db.DatabaseEntry, 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` or `SecondaryMultiKeyCreator` for many-to-many, one-to-many, many-to-one and one-to-one relationships.

- - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `nullifyForeignKey(SecondaryDatabase secondary, DatabaseEntry key, DatabaseEntry data, DatabaseEntry secKey)` Sets the foreign key reference to null in the datum of the primary database.

- - ### Method Detail

    - #### nullifyForeignKey

          boolean nullifyForeignKey(SecondaryDatabase secondary,
                                    DatabaseEntry key,
                                    DatabaseEntry data,
                                    DatabaseEntry secKey)
                             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.
        `key` - the existing primary key. 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.
        `secKey` - the secondary key to be nullified. This parameter is needed for knowing which key to nullify when multiple keys are present, as when `SecondaryMultiKeyCreator` is used.
      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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