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// $Id: MapKeyJoinColumn.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 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( { 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.
         * 
         *  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 "";
}