Copyright (c) 2008 - 2013 Oracle Corporation. 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 2.1
Linda DeMichiel - Java Persistence 2.0
/*******************************************************************************
* Copyright (c) 2008 - 2013 Oracle Corporation. 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 2.1
* Linda DeMichiel - Java Persistence 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;
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
/**
* 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.
*
* <p> 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.
*
* <p> The {@link MapKeyClass} annotation is not used when
* <code>MapKey</code> is specified and vice versa.
*
* <pre>
*
* 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() { ... }
* ...
* }
* </pre>
*
* @since Java Persistence 1.0
*/
@Target({METHOD, 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.
/**
* (Optional) The name of the persistent field or property of the
* associated entity that is used as the map key.
* <p> Default: If the
* <code>name</code> 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 <code>IdClass</code>, an instance of the primary key
* class is used as the key.
*/
String name() default "";
}