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/*
 * Copyright (c) 2008, 2023 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 {@code MapKeyJoinColumn}
 * annotation is specified, a single join column is assumed and the default
 * values apply.
 *
 * 

Example 1: * {@snippet : * @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 organization; * } * } * *

Example 2: * {@snippet : * @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 videoInventory; * ... * } * * @Entity * public class Movie { * @Id long id; * String title; * ... * } * } * *

Example 3: * {@snippet : * @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 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 {@link ManyToMany} * entity relationship or for a {@link OneToMany} entity * relationship using a join table, the foreign key column * is in a join table. *
  • If the join is for a {@link 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; "{@code _}"; "{@code 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 {@link 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) A SQL fragment appended to the generated DDL * which declares this column. May not be used in * conjunction with {@link #columnDefinition()}. * * @since 3.2 */ String options() 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 {@link ManyToMany} * entity relationship or for a {@link OneToMany} entity * relationship using a join table, the foreign key column * is in a join table. *
  • If the join is for a {@link 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 {@link OneToMany} or {@link ManyToMany} * entity relationship using a join table, the name of the join * table for the map. *
  • If the map is for a {@link 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, a default foreign key * strategy is selected by the persistence provider. * * @since 2.1 */ ForeignKey foreignKey() default @ForeignKey(ConstraintMode.PROVIDER_DEFAULT); }




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