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/*
* Copyright (c) 2011, 2018 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 org.eclipse.persistence.expressions.Expression;
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:
* <ul>
* <li> It must extend the org.eclipse.persistence.descriptors.ClassExtractor
* class and implement the extractClassFromRow(Record, Session) method.
* <li> That method must take a database row (a Record/Map) as an argument and
* must return the class to use for that row.
* </ul>
* 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.
* <p>
* 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 SINGLE_TABLE and JOINED inheritance
* strategies.
* <p>
* If a ClassExtractor is used then a DiscriminatorColumn cannot be used. A
* DiscriminatorColumn also cannot be used on either the root or its subclasses.
* <p>
* In addition, for more complex configurations using a ClassExtractor and a
* 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(Expression)
* @see org.eclipse.persistence.descriptors.InheritancePolicy#setOnlyInstancesExpression(Expression)
*
* @author Guy Pelletier
* @since EclipseLink 2.1
*/
@Target({TYPE})
@Retention(RUNTIME)
public @interface ClassExtractor {
/**
* (Required) Defines the name of the class extractor that should be
* applied to this entity's descriptor.
*/
Class<? extends org.eclipse.persistence.descriptors.ClassExtractor> value();
}
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