/*******************************************************************************
 * Copyright (c) 2008 - 2015 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:
 *     Petros Splinakis - Java Persistence 2.2
 *     Linda DeMichiel - Java Persistence 2.1
 *     Linda DeMichiel - Java Persistence 2.0
 *
 ******************************************************************************/ 
package javax.persistence;

import java.lang.annotation.Repeatable;
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;
import static javax.persistence.ConstraintMode.PROVIDER_DEFAULT;

/**
 * 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
 * <code>MapKeyJoinColumn</code> annotation is specified, a single
 * join column is assumed and the default values apply.
 *
 * <pre>
 *
 *    Example 1:
 *
 *    &#064;Entity
 *    public class Company {
 *       &#064;Id int id;
 *       ...
 *       &#064;OneToMany   // unidirectional
 *       &#064;JoinTable(name="COMPANY_ORGANIZATION",
 *                  joinColumns=&#064;JoinColumn(name="COMPANY"),
 *                  inverseJoinColumns=&#064;JoinColumn(name="VICEPRESIDENT"))
 *       &#064;MapKeyJoinColumn(name="DIVISION")
 *       Map&#060;Division, VicePresident&#062; organization;
 *    }
 *
 *    Example 2:
 *
 *    &#064;Entity
 *    public class VideoStore {
 *       &#064;Id int id;
 *       String name;
 *       Address location;
 *       ...
 *       &#064;ElementCollection
 *       &#064;CollectionTable(name="INVENTORY",
 *                        joinColumns=&#064;JoinColumn(name="STORE"))
 *       &#064;Column(name="COPIES_IN_STOCK")
 *       &#064;MapKeyJoinColumn(name="MOVIE", referencedColumnName="ID")
 *       Map&#060;Movie, Integer&#062; videoInventory;
 *       ...
 *     }
 *
 *     &#064;Entity
 *     public class Movie {
 *        &#064;Id long id;
 *        String title;
 *        ...
 *     }
 *
 *     Example 3:
 *
 *     &#064;Entity
 *     public class Student {
 *        &#064;Id int studentId;
 *        ...
 *        &#064;ManyToMany  // students and courses are also many-many
 *        &#064;JoinTable(name="ENROLLMENTS",
 *                   joinColumns=&#064;JoinColumn(name="STUDENT"),
 *                   inverseJoinColumns=&#064;JoinColumn(name="SEMESTER"))
 *        &#064;MapKeyJoinColumn(name="COURSE")
 *        Map&#060;Course, Semester&#062;  enrollment;
 *        ...
 *     }
 * </pre>
 *
 * @see ForeignKey
 *
 * @since Java Persistence 2.0
 */
@Repeatable(MapKeyJoinColumns.class)
@Target( { METHOD, FIELD })
@Retention(RUNTIME)
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.  
         * <ul> 
         * <li> 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.  
         * <li> 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. 
         * <li> 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.
         * </ul>
         *
         * <p> 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.
         *
         * <p> 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 <code>UniqueConstraint</code> 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. 
         * <ul>
         * <li> 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. 
         * <li> 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.
	 * <li> 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.
         * </ul>
         * <p> Default: 
         * <ul>
         * <li> If the map is for an element collection, the
         * name of the collection table for the map value.
         * <li> If the map is for a OneToMany or ManyToMany entity relationship 
         * using a join table, the name of the join table for the map. 
         * <li> 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.
         * </ul>
	 */
	String table() default "";

        /**
         *  (Optional) Used to specify or control the generation of a
         *  foreign key constraint when table generation is in effect.  If
         *  this element is not specified, the persistence provider's
         *  default foreign key strategy will apply.
         *
         *  @since Java Persistence 2.1
         */
        ForeignKey foreignKey() default @ForeignKey(PROVIDER_DEFAULT);
}