foundation/org.eclipse.persistence.core/src/main/java/org/eclipse/persistence/annotations/BatchFetchType.java

/*
 * Copyright (c) 2011, 2020 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:
//     James Sutherland - initial implementation
package org.eclipse.persistence.annotations;

import org.eclipse.persistence.mappings.ForeignReferenceMapping;

/**
 * Enum used with the BatchFetch annotation, or "eclipselink.batch.type" query hint.
 * This can be specified on a mapping or query to configure the type of batch reading to be used.
 *
 * @see BatchFetch
 * @see ForeignReferenceMapping#setBatchFetchType(BatchFetchType)
 * @author James Sutherland
 * @since EclipseLink 2.1
 */
public enum BatchFetchType {
    /**
     * This is the default form of batch reading.
     * The original query's selection criteria is joined with the batch query.
     */
    JOIN,

    /**
     * This uses an SQL EXISTS and a sub-select in the batch query instead of a join.
     * This has the advantage of not requiring an SQL DISTINCT which can have issues
     * with LOBs, or may be more efficient for some types of queries or on some databases.
     */
    EXISTS,

    /**
     * This uses an SQL IN clause in the batch query passing in the source object Ids.
     * This has the advantage of only selecting the objects not already contained in the cache,
     * and can work better with cursors, or if joins cannot be used.
     * This may only work for singleton Ids on some databases.
     */
    IN
}