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/*******************************************************************************
 * Copyright (c) 2011 - 2017 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:
 *     Linda DeMichiel - Java Persistence 2.1
 *
 ******************************************************************************/
package javax.persistence;

import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static javax.persistence.ConstraintMode.CONSTRAINT;

/**
 * Used to specify the handling of foreign key constraints when schema
 * generation is in effect.  If this annotation is not specified, the
 * persistence provider's default foreign key strategy will be used.
 * 
 * The ConstraintMode value is used to specify whether foreign
 * key constraints should be generated.
 * 

 * The syntax used in the foreignKeyDefinition element 
 * should follow the SQL syntax used by the target database for foreign
 * key constraints.  For example, this may be similar the following:
 * 
 * FOREIGN KEY ( <COLUMN expression> {, <COLUMN expression>}... )
 * REFERENCES <TABLE identifier> [
 *     (<COLUMN expression> {, <COLUMN expression>}... ) ]
 * [ ON UPDATE <referential action> ]
 * [ ON DELETE <referential action> ]
 * 
 *
 * When the ConstraintMode value is
 * CONSTRAINT, but the foreignKeyDefinition
 * element is not specified, the provider will generate foreign key
 * constraints whose update and delete actions it determines most
 * appropriate for the join column(s) to which the foreign key
 * annotation is applied.
 *
 * @see JoinColumn
 * @see JoinColumns
 * @see MapKeyJoinColumn
 * @see MapKeyJoinColumns
 * @see PrimaryKeyJoinColumn
 * @see JoinTable
 * @see CollectionTable
 * @see SecondaryTable
 * @see AssociationOverride
 *
 * @since Java Persistence 2.1
 */
@Target({})
@Retention(RUNTIME)
public @interface ForeignKey {

    /**
     * (Optional) The name of the foreign key constraint.  If this
     * is not specified, it defaults to a provider-generated name.
     */
    String name() default "";

    /**
     * (Optional) Used to specify whether a foreign key constraint should be
     *  generated when schema generation is in effect. 
     *  
     *  A value of CONSTRAINT will cause the persistence
     *  provider to generate a foreign key constraint.  If the
     *  foreignKeyDefinition element is not specified, the
     *  provider will generate a constraint whose update
     *  and delete actions it determines most appropriate for the
     *  join column(s) to which the foreign key annotation is applied.
     *  

     *  A value of NO_CONSTRAINT will result in no
     *  constraint being generated.
     *  
     *  A value of PROVIDER_DEFAULT will result in the
     *  provider's default behavior (which may or may not result
     *  in the generation of a constraint for the given join column(s).
     */
    ConstraintMode value() default CONSTRAINT;

    /**
     * (Optional) The foreign key constraint definition.  
     */
    String foreignKeyDefinition() default "";
}