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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: MapKeyColumn.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 mapping for the key column of a map whose map key is a basic type. If the name element is not specified, it defaults to the concatenation of the following: the name of the referencing relationship field or property; "_"; "KEY".
    Example:

    @Entity
    public class Item {
       @Id int id;
       ...
       @ElementCollection
       @MapKeyColumn(name="IMAGE_NAME")
       @Column(name="IMAGE_FILENAME")
       @CollectionTable(name="IMAGE_MAPPING")
       Map<String, String> images;  // map from image name to filename
       ...
    }
 

Since:
Java Persistence 2.0
 
 @Target( {  })
 public @interface MapKeyColumn {

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

Defaults to the concatenation of the following: the name of the referencing relationship field or property; "_"; "KEY".

 
 	String name() default "";

(Optional) Whether the column 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 corresponds to only a single column. This constraint applies in addition to any constraint entailed by primary key mapping and to constraints specified at the table level.
 
 	boolean unique() default false;

(Optional) Whether the database 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 the generated SQL to create a column of the inferred type.

 
	String columnDefinition() default "";

(Optional) The name of the table that contains the column.

Defaults: If the map key is for an element collection, the name of the collection table for the map value. If the map key is for a OneToMany or ManyToMany entity relationship using a join table, the name of the join table for the map. If the map key 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 "";

(Optional) The column length. (Applies only if a string-valued column is used.)
	int length() default 255;

(Optional) The precision for a decimal (exact numeric) column. (Applies only if a decimal column is used.)

Default: 0. (The value must be set by the developer.)

	int precision() default 0; // decimal precision
(Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)
	int scale() default 0; // decimal scale
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