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/*
 * Copyright (c) 2008, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Petros Splinakis - 2.2
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0

package jakarta.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;

/**
 * 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;
 *        ...
 *     }
 * 
* * @see ForeignKey * * @since 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. *
    *
  • 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 ""; /** * (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 2.1 */ ForeignKey foreignKey() default @ForeignKey(ConstraintMode.PROVIDER_DEFAULT); }




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