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The Java Persistence API (JPA) : a standard interface-based Java model abstraction of persistence, developed by the JCP.
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/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. 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.
 */
package javax.persistence;

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

import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
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.FetchType.LAZY;

/**
 * Defines a many-valued association with one-to-many multiplicity.
 * 
 * If the collection is defined using generics to specify the element type, the associated target entity type
 * need not be specified; otherwise the target entity class must be specified. If the relationship is
 * bidirectional, the  mappedBy element must be used to specify the relationship field or
 * property of the entity that is the owner of the relationship.
 * 

 * The OneToMany annotation may be used within an embeddable class contained within an entity
 * class to specify a relationship to a collection of entities. If the relationship is bidirectional, the
 *  mappedBy element must be used to specify the relationship field or property of the entity
 * that is the owner of the relationship. When the collection is a java.util.Map, the
 * cascade element and the orphanRemoval element apply to the map value.
 *
 * 
 *
 *    Example 1: One-to-Many association using generics
 * 
 *    // In Customer class:
 * 
 *    @OneToMany(cascade=ALL, mappedBy="customer")
 *    public Set<Order> getOrders() { return orders; }
 * 
 *    In Order class:
 * 
 *    @ManyToOne
 *    @JoinColumn(name="CUST_ID", nullable=false)
 *    public Customer getCustomer() { return customer; }
 * 
 * 
 *    Example 2: One-to-Many association without using generics
 * 
 *    // In Customer class:
 * 
 *    @OneToMany(targetEntity=com.acme.Order.class, cascade=ALL,
 *                mappedBy="customer")
 *    public Set getOrders() { return orders; }
 * 
 *    // In Order class:
 * 
 *    @ManyToOne
 *    @JoinColumn(name="CUST_ID", nullable=false)
 *    public Customer getCustomer() { return customer; }
 * 
 * 
 *    Example 3: Unidirectional One-to-Many association using a foreign key mapping
 * 
 *    // In Customer class:
 * 
 *    @OneToMany(orphanRemoval=true)
 *    @JoinColumn(name="CUST_ID") // join column is in table for Order
 *    public Set<Order> getOrders() {return orders;}
 *
 * 
 * @since Java Persistence 1.0
 */
@Target({ANNOTATION_TYPE, METHOD, FIELD})
@Retention(RUNTIME)
public @interface OneToMany
{

    /**
     * (Optional) The entity class that is the target of the association. Optional only if the collection
     * property is defined using Java generics. Must be specified otherwise.
     * 
     * Defaults to the parameterized type of the collection when defined using generics.
     * @return target entity
     */
    Class targetEntity() default void.class;

    /**
     * (Optional) The operations that must be cascaded to the target of the association.
     * 

     * Defaults to no operations being cascaded.
     * 
     * When the target collection is a {@link java.util.Map java.util.Map}, the cascade element
     * applies to the map value.
     * @return cascade type
     */
    CascadeType[] cascade() default {};

    /**
     * (Optional) Whether the association should be lazily loaded or must be eagerly fetched. The EAGER
     * strategy is a requirement on the persistence provider runtime that the associated entities must be
     * eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.
     * @return The fetch type
     */
    FetchType fetch() default LAZY;

    /**
     * The field that owns the relationship. Required unless the relationship is unidirectional.
     * @return mappedby
     */
    String mappedBy() default "";

    /**
     * (Optional) Whether to apply the remove operation to entities that have been removed from the
     * relationship and to cascade the remove operation to those entities.
     * @since Java Persistence 2.0
     * @return whether to remove orphans
     */
    boolean orphanRemoval() default false;
}