Java tutorial
/******************************************************************************* * 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: * * @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; * ... * } * </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); }