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  /*
   * 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: MapKeyJoinColumn.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 a mapping to an entity that is a map key. The map key join column is in the collection table, join table, or table of the target entity that is used to represent the map. If no MapKeyJoinColumn annotation is specified, a single join column is assumed and the default values apply.

    Example 1:

    @Entity
    public class Company {
       @Id int id;
       ...
       @OneToMany   // unidirectional
       @JoinTable(name="COMPANY_ORGANIZATION",
                  joinColumns=@JoinColumn(name="COMPANY"),
                  inverseJoinColumns=@JoinColumn(name="VICEPRESIDENT"))
       @MapKeyJoinColumn(name="DIVISION")
       Map<Division, VicePresident> organization;
    }

    Example 2:

    @Entity
    public class VideoStore {
       @Id int id;
       String name;
       Address location;
       ...
       @ElementCollection
       @CollectionTable(name="INVENTORY",
                        joinColumns=@JoinColumn(name="STORE"))
       @Column(name="COPIES_IN_STOCK")
       @MapKeyJoinColumn(name="MOVIE", referencedColumnName="ID")
       Map<Movie, Integer> videoInventory;
       ...
     }

     @Entity
     public class Movie {
        @Id long id;
        String title;
        ...
     }

     Example 3:

     @Entity
     public class Student {
        @Id int studentId;
        ...
        @ManyToMany  // students and courses are also many-many
        @JoinTable(name="ENROLLMENTS",
                   joinColumns=@JoinColumn(name="STUDENT"),
                   inverseJoinColumns=@JoinColumn(name="SEMESTER"))
        @MapKeyJoinColumn(name="COURSE")
        Map<Course, Semester>  enrollment;
        ...
     }
 

Since:
Java Persistence 2.0
 
 @Target( {  })
 public @interface MapKeyJoinColumn {
(Optional) The name of the foreign key column for the map key. The table in which it is found depends upon the context.
  • If the join is for a map key for an element collection, the foreign key column is in the collection table for the map value.
  • If the join is for a map key for a ManyToMany entity relationship or for a OneToMany entity relationship using a join table, the foreign key column is in a join table.
  • If the join is for a OneToMany entity relationship using a foreign key mapping strategy, the foreign key column for the map key is in the table of the entity that is the value of the map.

Default (only applies if a single join column is used.) The concatenation of the following: the name of the referencing relationship property or field of the referencing entity or embeddable class; "_"; "KEY".

	String name() default "";

(Optional) The name of the column referenced by this foreign key column. The referenced column is in the table of the target entity.

Default (only applies if single join column is being used.) The same name as the primary key column of the referenced table

	String referencedColumnName() default "";

(Optional) Whether the property is a unique key. This is a shortcut for the UniqueConstraint annotation at the table level and is useful for when the unique key constraint is only a single field.
	boolean unique() default false;

(Optional) Whether the foreign key column is nullable.
	boolean nullable() default false;

(Optional) Whether the column is included in SQL INSERT statements generated by the persistence provider.
	boolean insertable() default true;

(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence provider.
	boolean updatable() default true;

(Optional) The SQL fragment that is used when generating the DDL for the column. Defaults to SQL generated by the provider for the column.
	String columnDefinition() default "";

(Optional) The name of the table that contains the foreign key column.
  • If the join is for a map key for an element collection, the foreign key column is in the collection table for the map value.
  • If the join is for a map key for a ManyToMany entity relationship or for a OneToMany entity relationship using a join table, the foreign key column is in a join table.
  • If the join is for a OneToMany entity relationship using a foreign key mapping strategy, the foreign key column for the map key is in the table of the entity that is the value of the map.

Default:

  • If the map is for an element collection, the name of the collection table for the map value.
  • If the map is for a OneToMany or ManyToMany entity relationship using a join table, the name of the join table for the map.
  • If the map is for a OneToMany entity relationship using a foreign key mapping strategy, the name of the primary table of the entity that is the value of the map.
	String table() default "";
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