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/*
 * Copyright (c) 2011, 2024 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     12/18/2009-2.1 Guy Pelletier
//       - 211323: Add class extractor support to the EclipseLink-ORM.XML Schema
package org.eclipse.persistence.annotations;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * A ClassExtractor allows for a user defined class indicator in place of
 * providing a discriminator column. The class has the following restrictions:
 * 
    *
  • It must extend the {@linkplain org.eclipse.persistence.descriptors.ClassExtractor} class and implement the * {@linkplain org.eclipse.persistence.descriptors.ClassExtractor#extractClassFromRow(org.eclipse.persistence.sessions.DataRecord, org.eclipse.persistence.sessions.Session)} * method.
  • *
  • That method must take a database row (a {@linkplain org.eclipse.persistence.sessions.DataRecord}/Map) as an argument and * must return the class to use for that row.
  • *
* This method will be used to decide which class to instantiate when reading * from the database. It is the application's responsibility to populate any * typing information in the database required to determine the class from the * row. *

* The ClassExtractor must only be set on the root of an entity class or * sub-hierarchy in which a different inheritance strategy is applied. The * ClassExtractor can only be used with the {@linkplain jakarta.persistence.InheritanceType#SINGLE_TABLE} * and {@linkplain jakarta.persistence.InheritanceType#JOINED} inheritance * strategies. *

* If a ClassExtractor is used then a {@linkplain jakarta.persistence.DiscriminatorColumn} cannot be used. A * {@linkplain jakarta.persistence.DiscriminatorColumn} also cannot be used on either the root or its subclasses. *

* In addition, for more complex configurations using a ClassExtractor and * an {@linkplain jakarta.persistence.InheritanceType#SINGLE_TABLE} strategy, the descriptor's withAllSubclasses and onlyInstances * expressions should be set through the ClassExtractor's initialize method. * * @see org.eclipse.persistence.descriptors.ClassExtractor * @see org.eclipse.persistence.descriptors.InheritancePolicy#setWithAllSubclassesExpression(org.eclipse.persistence.expressions.Expression) * @see org.eclipse.persistence.descriptors.InheritancePolicy#setOnlyInstancesExpression(org.eclipse.persistence.expressions.Expression) * * @author Guy Pelletier * @since EclipseLink 2.1 */ @Target({TYPE}) @Retention(RUNTIME) public @interface ClassExtractor { /** * Defines the name of the class extractor that should be * applied to this entity's descriptor. */ Class value(); }





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