Start line:  
End line:  

Snippet Preview

Snippet HTML Code

Stack Overflow Questions
  /*
   * Copyright (c) 2008, 2009 Sun Microsystems. 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.
  *
  * Contributors:
  *     Linda DeMichiel - Java Persistence 2.0 - Version 2.0 (October 1, 2009)
  *     Specification available from http://jcp.org/en/jsr/detail?id=317
  */
 
 // $Id: MapKey.java 20957 2011-06-13 09:58:51Z stliu $
 
 package javax.persistence;
 
 import static java.lang.annotation.ElementType.FIELD;
 import static java.lang.annotation.ElementType.METHOD;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;

Specifies the map key for associations of type java.util.Map when the map key is itself the primary key or a persistent field or property of the entity that is the value of the map.

If a persistent field or property other than the primary key is used as a map key then it is expected to have a uniqueness constraint associated with it.

The MapKeyClass annotation is not used when MapKey is specified and vice versa.


    Example 1:

    @Entity
    public class Department {
        ...
        @OneToMany(mappedBy="department")
        @MapKey  // map key is primary key
        public Map<Integer, Employee> getEmployees() {... }
        ...
    }

    @Entity
    public class Employee {
        ...
        @Id Integer getEmpId() { ... }
        @ManyToOne
        @JoinColumn(name="dept_id")
        public Department getDepartment() { ... }
        ...
    }

    Example 2:

    @Entity
        public class Department {
        ...
        @OneToMany(mappedBy="department")
        @MapKey(name="name")
        public Map<String, Employee> getEmployees() {... }
        ...
    }

    @Entity
        public class Employee {
        @Id public Integer getEmpId() { ... }
        ...
        @ManyToOne
        @JoinColumn(name="dept_id")
        public Department getDepartment() { ... }
        ...
    }
 

Since:
Java Persistence 1.0
 
 public @interface MapKey {

    
(Optional) The name of the persistent field or property of the associated entity that is used as the map key.

Default: If the name element is not specified, the primary key of the associated entity is used as the map key. If the primary key is a composite primary key and is mapped as IdClass, an instance of the primary key class is used as the key.

 
    String name() default "";
New to GrepCode? Check out our FAQ X