src/javax/persistence/MapsId.java

/*
 * Copyright (c) 2008, 2019 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:
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0

package javax.persistence;

import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Designates a <code>ManyToOne</code> or
 * <code>OneToOne</code> relationship attribute that provides the
 * mapping for an {@link EmbeddedId} primary key, an attribute within
 * an <code>EmbeddedId</code> primary key, or a simple primary key of
 * the parent entity. The <code>value</code> element specifies the
 * attribute within a composite key to which the relationship
 * attribute corresponds. If the entity's primary key is of the same
 * Java type as the primary key of the entity referenced by the
 * relationship, the value attribute is not specified.
 * 
 * <pre>
 *    Example:
 *
 *    // parent entity has simple primary key
 *
 *    &#064;Entity
 *    public class Employee {
 *       &#064;Id long empId;
 *       String name;
 *       ...
 *    } 
 *
 *    // dependent entity uses EmbeddedId for composite key
 *
 *    &#064;Embeddable
 *    public class DependentId {
 *       String name;
 *       long empid;   // corresponds to primary key type of Employee
 *    }
 *
 *    &#064;Entity
 *    public class Dependent {
 *       &#064;EmbeddedId DependentId id;
 *        ...
 *       &#064;MapsId("empid")  //  maps the empid attribute of embedded id
 *       &#064;ManyToOne Employee emp;
 *    }
 * </pre>
 *
 * @since 2.0
 */
@Target( { METHOD, FIELD })
@Retention(RUNTIME)
public @interface MapsId {

    /**
     * (Optional) The name of the attribute within the composite key
     * to which the relationship attribute corresponds.  If not
     * supplied, the relationship maps the entity's primary
     * key.
     */
   String value() default ""; }