foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/descriptors/ClassExtractor.java

/*
 * Copyright (c) 1998, 2021 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:
//     Oracle - initial API and implementation from Oracle TopLink
package org.eclipse.persistence.descriptors;

import org.eclipse.persistence.exceptions.*;
import org.eclipse.persistence.sessions.*;

/**
 * <p><b>Purpose</b>:
 * Abstract class to allow complex inheritance support.  Typically class indicators are used to define inheritance in the database,
 * however in complex cases the class type may be determined through another mechanism.
 * The class extractor must be able to determine and return the class type from the database row.
 *
 * @see org.eclipse.persistence.descriptors.InheritancePolicy#setClassExtractor(ClassExtractor)
 */
public abstract class ClassExtractor {

    /**
     * Extract/compute the class from the database row and return the class.
     * Map is used as the public interface to database row, the key is the field name,
     * the value is the database value.
     */
    public abstract <T> Class<T> extractClassFromRow(DataRecord databaseRow, Session session);

    /**
     * Allow for any initialization.
     */
    public void initialize(ClassDescriptor descriptor, Session session) throws DescriptorException {
        // Do nothing by default.
    }
}