/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.  The Eclipse Public License is available
 * at http://www.eclipse.org/legal/epl-v10.html and the Eclipse Distribution License
 * is available at http://www.eclipse.org/org/documents/edl-v10.php.
 */
package javax.persistence;

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

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

Designates a ManyToOne or OneToOne relationship attribute that provides the mapping for an EmbeddedId primary key, an attribute within an EmbeddedId primary key,
or a simple primary key of the parent entity. The value 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.

   Example:
   // parent entity has simple primary key
   @Entity
   public class Employee {
      @Id long empId;
      String name;
      ...
   }
   // dependent entity uses EmbeddedId for composite key
   @Embeddable
   public class DependentId {
      String name;
      long empid;   // corresponds to primary key type of Employee
   }
   @Entity
   public class Dependent {
      @EmbeddedId DependentId id;
       ...
      @MapsId("empid")  //  maps the empid attribute of embedded id
      @ManyToOne Employee emp;
   }

Since:
Java Persistence 2.0/**
 * 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.
 * <p>
 * <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 Java Persistence 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 entitys primary key.
Returns:
name/**
   * (Optional) The name of the attribute within the composite key to which the relationship attribute
   * corresponds. If not supplied, the relationship maps the entitys primary key.
   *
   * @return name
   */
  String value() default "";
}