/*
 * 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 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/**
 * Specifies the mapping for the key column of a map whose map key is a basic type. If the <code>name</code>
 * element is not specified, it defaults to the concatenation of the following: the name of the referencing
 * relationship field or property; "_"; "KEY".
 * <p>
 * <pre>
 *    Example:
 *
 *    &#064;Entity
 *    public class Item {
 *       &#064;Id int id;
 *       ...
 *       &#064;ElementCollection
 *       &#064;MapKeyColumn(name="IMAGE_NAME")
 *       &#064;Column(name="IMAGE_FILENAME")
 *       &#064;CollectionTable(name="IMAGE_MAPPING")
 *       Map&#060;String, String&#062; images;  // map from image name to filename
 *       ...
 *    }
 * </pre>
 *
 * @since Java Persistence 2.0
 */
@Target({FIELD})
@Retention(RUNTIME)
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".
Returns:
The name/**
   * (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.
   * <p>
   * Defaults to the concatenation of the following: the name of the referencing relationship field or
   * property; "_"; "<code>KEY</code>".
   *
   * @return The name
   */
  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.
Returns:
Whether unique/**
   * (Optional) Whether the column is a unique key. This is a shortcut for the <code>UniqueConstraint</code>
   * 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.
   *
   * @return Whether unique
   */
  boolean unique() default false;

  
(Optional) Whether the database column is nullable.
Returns:
Whether nullable/**
   * (Optional) Whether the database column is nullable.
   *
   * @return Whether nullable
   */
  boolean nullable() default false;

  
(Optional) Whether the column is included in SQL INSERT statements generated by the persistence
provider.
Returns:
Whether insertable/**
   * (Optional) Whether the column is included in SQL INSERT statements generated by the persistence
   * provider.
   *
   * @return Whether insertable
   */
  boolean insertable() default true;

  
(Optional) Whether the column is included in SQL UPDATE statements generated by the persistence
provider.
Returns:
Whether updateable/**
   * (Optional) Whether the column is included in SQL UPDATE statements generated by the persistence
   * provider.
   *
   * @return Whether updateable
   */
  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.
Returns:
The column definition/**
   * (Optional) The SQL fragment that is used when generating the DDL for the column.
   * <p>
   * Defaults to the generated SQL to create a column of the inferred type.
   *
   * @return The column definition
   */
  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.
Returns:
The table/**
   * (Optional) The name of the table that contains the column.
   * <p>
   * 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.
   *
   * @return The table
   */
  String table() default "";

  
(Optional) The column length. (Applies only if a string-valued column is used.)
Returns:
The length/**
   * (Optional) The column length. (Applies only if a string-valued column is used.)
   *
   * @return The length
   */
  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.)
Returns:
The precision/**
   * (Optional) The precision for a decimal (exact numeric) column. (Applies only if a decimal column is
   * used.)
   * <p>
   * Default: 0. (The value must be set by the developer.)
   *
   * @return The precision
   */
  int precision() default 0; // decimal precision

  
(Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)
Returns:
The scale/**
   * (Optional) The scale for a decimal (exact numeric) column. (Applies only if a decimal column is used.)
   *
   * @return The scale
   */
  int scale() default 0; // decimal scale
}