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.METHOD; import static java.lang.annotation.ElementType.FIELD; import static java.lang.annotation.ElementType.TYPE; import static java.lang.annotation.RetentionPolicy.RUNTIME; import static javax.persistence.ConstraintMode.PROVIDER_DEFAULT; /** * Specifies a primary key column that is used as a foreign key to * join to another table. * * <p> It is used to join the primary table of an entity subclass * in the {@link InheritanceType#JOINED JOINED} mapping strategy * to the primary table of its superclass; it is used within a * {@link SecondaryTable} annotation to join a secondary table * to a primary table; and it may be used in a {@link OneToOne} * mapping in which the primary key of the referencing entity * is used as a foreign key to the referenced entity. * * <p> If no <code>PrimaryKeyJoinColumn</code> annotation is * specified for a subclass in the <code>JOINED</code> * mapping strategy, the foreign key columns are assumed * to have the same names as the primary key columns of the * primary table of the superclass. * * <pre> * * Example: Customer and ValuedCustomer subclass * * @Entity * @Table(name="CUST") * @Inheritance(strategy=JOINED) * @DiscriminatorValue("CUST") * public class Customer { ... } * * @Entity * @Table(name="VCUST") * @DiscriminatorValue("VCUST") * @PrimaryKeyJoinColumn(name="CUST_ID") * public class ValuedCustomer extends Customer { ... } * </pre> * * @see SecondaryTable * @see Inheritance * @see OneToOne * @see ForeignKey * * @since Java Persistence 1.0 */ @Repeatable(PrimaryKeyJoinColumns.class) @Target({ TYPE, METHOD, FIELD }) @Retention(RUNTIME) public @interface PrimaryKeyJoinColumn { /** * (Optional) The name of the primary key column of the current table. * <p> Defaults to the same name as the primary key column * of the primary table of the superclass (<code>JOINED</code> mapping strategy); the same * name as the primary key column of the primary table * (<code>SecondaryTable</code> mapping); or the same name as the * primary key column for the table for the referencing entity * (<code>OneToOne</code> mapping). */ String name() default ""; /** * (Optional) The name of the primary key column of the table * being joined to. <p> Defaults to the same name as the primary * key column of the primary table of the superclass * (<code>JOINED</code> mapping strategy); the same name as the * primary key column of the primary table * (<code>SecondaryTable</code> mapping); or the same name as the * primary key column for the table for the referencing entity * (<code>OneToOne</code> mapping). */ String referencedColumnName() default ""; /** * (Optional) The SQL fragment that is used when generating the * DDL for the column. This should not be specified for a * <code>OneToOne</code> primary key association. * <p> Defaults to the generated SQL to create a column of the * inferred type. */ String columnDefinition() default ""; /** * (Optional) Used to specify or control the generation of a * foreign key constraint for the primary key join column * 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); }