javax.persistence.MapKey Maven / Gradle / Ivy
// $Id: MapKey.java 17752 2009-10-15 01:19:21Z [email protected] $
// EJB3 Specification Copyright 2004-2009 Sun Microsystems, Inc.
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
* {@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({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.
*/
String name() default "";
}