javax.persistence.PrimaryKeyJoinColumn Maven / Gradle / Ivy

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package javax.persistence;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Specifies a primary key column that is used as a foreign key to join to another table.
 * 
 * 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.
 * 

 * If no PrimaryKeyJoinColumn annotation is specified for a subclass in the JOINED 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.
 * 
 * 
 * 
 *    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 { ... }
 * 
 * 
 * @see SecondaryTable
 * @see Inheritance
 * @see OneToOne
 * @since Java Persistence 1.0
 */
@Target({ TYPE, METHOD, FIELD })
@Retention(RUNTIME)
public @interface PrimaryKeyJoinColumn {

	/**
	 * (Optional) The SQL fragment that is used when generating the DDL for the column. This should not be specified for a
	 * OneToOne primary key association.
	 * 
	 * Defaults to the generated SQL to create a column of the inferred type.
	 */
	String columnDefinition() default "";

	/**
	 * (Optional) The name of the primary key column of the current table.
	 * 

	 * Defaults to the same name as the primary key column of the primary table of the superclass (JOINED mapping strategy);
	 * the same name as the primary key column of the primary table (SecondaryTable mapping); or the same name as the primary
	 * key column for the table for the referencing entity (OneToOne mapping).
	 */
	String name() default "";

	/**
	 * (Optional) The name of the primary key column of the table being joined to.
	 * 
	 * Defaults to the same name as the primary key column of the primary table of the superclass (JOINED mapping strategy);
	 * the same name as the primary key column of the primary table (SecondaryTable mapping); or the same name as the primary
	 * key column for the table for the referencing entity (OneToOne mapping).
	 */
	String referencedColumnName() default "";
}