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/*-
 * Copyright (C) 2002, 2018, Oracle and/or its affiliates. All rights reserved.
 *
 * This file was distributed by Oracle as part of a version of Oracle Berkeley
 * DB Java Edition made available at:
 *
 * http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/downloads/index.html
 *
 * Please see the LICENSE file included in the top-level directory of the
 * appropriate version of Oracle Berkeley DB Java Edition for a copy of the
 * license and additional information.
 */

package com.sleepycat.je;

/**
 * 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 {@link * ForeignKeyDeleteAction#NULLIFY}. The key nullifier is specified by calling * {@link SecondaryConfig#setForeignKeyNullifier}.

* *

When a referenced record in the foreign key database is deleted and the * foreign key delete action is NULLIFY, the {@link * ForeignKeyNullifier#nullifyForeignKey} 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 {@link SecondaryKeyCreator} for * many-to-one and one-to-one relationships. It may not be used with * {@link 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 {@link SecondaryMultiKeyCreator}, use * {@link ForeignMultiKeyNullifier} instead. */ public interface ForeignKeyNullifier { /** * Sets the foreign key reference to null in the datum of the primary * database. * * @param secondary the database in which the foreign key integrity * constraint is defined. This parameter is passed for informational * purposes but is not commonly used. * * @param 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. * * @return 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. */ public boolean nullifyForeignKey(SecondaryDatabase secondary, DatabaseEntry data) throws DatabaseException; }




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