javax.persistence.MapKey Maven / Gradle / Ivy
/*
* 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.RetentionPolicy.RUNTIME;
/**
* Specifies the map key for associations of type {@link java.util.Map 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 {@link 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
*/
@Target({FIELD})
@Retention(RUNTIME)
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.
*
* @return The name
*/
String name() default "";
}