001/*
002 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. All rights reserved.
003 *
004 * This program and the accompanying materials are made available under the
005 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
006 * which accompanies this distribution.  The Eclipse Public License is available
007 * at http://www.eclipse.org/legal/epl-v10.html and the Eclipse Distribution License
008 * is available at http://www.eclipse.org/org/documents/edl-v10.php.
009 */
010package javax.persistence;
011
012import java.lang.annotation.Retention;
013import java.lang.annotation.Target;
014
015import static java.lang.annotation.ElementType.FIELD;
016import static java.lang.annotation.RetentionPolicy.RUNTIME;
017import static javax.persistence.FetchType.LAZY;
018
019/**
020 * Defines a many-valued association with many-to-many multiplicity.
021 * <p>
022 * Every many-to-many association has two sides, the owning side and the non-owning, or inverse, side. The
023 * join table is specified on the owning side. If the association is bidirectional, either side may be
024 * designated as the owning side. If the relationship is bidirectional, the non-owning side must use the
025 * <code>mappedBy</code> element of the <code>ManyToMany</code> annotation to specify the relationship field
026 * or property of the owning side.
027 * <p>
028 * The join table for the relationship, if not defaulted, is specified on the owning side.
029 * <p>
030 * The <code>ManyToMany</code> annotation may be used within an embeddable class contained within an entity
031 * class to specify a relationship to a collection of entities. If the relationship is bidirectional and the
032 * entity containing the embeddable class is the owner of the relationship, the non-owning side must use the
033 * <code>mappedBy</code> element of the <code>ManyToMany</code> annotation to specify the relationship field
034 * or property of the embeddable class. The dot (".") notation syntax must be used in the
035 * <code>mappedBy</code> element to indicate the relationship attribute within the embedded attribute. The
036 * value of each identifier used with the dot notation is the name of the respective embedded field or
037 * property.
038 * <p>
039 * <pre>
040 *
041 *    Example 1:
042 *
043 *    // In Customer class:
044 *
045 *    &#064;ManyToMany
046 *    &#064;JoinTable(name="CUST_PHONES")
047 *    Set&#060;PhoneNumber&#062; phones;
048 *
049 *    // In PhoneNumber class:
050 *
051 *    &#064;ManyToMany(mappedBy="phones")
052 *    Set&#060;Customer&#062; customers;
053 *
054 *    Example 2:
055 *
056 *    // In Customer class:
057 *
058 *    &#064;ManyToMany(targetEntity=com.acme.PhoneNumber.class)
059 *    Set phones;
060 *
061 *    // In PhoneNumber class:
062 *
063 *    &#064;ManyToMany(targetEntity=com.acme.Customer.class, mappedBy="phones")
064 *    Set customers;
065 *
066 *    Example 3:
067 *
068 *    // In Customer class:
069 *
070 *    &#064;ManyToMany
071 *    &#064;JoinTable(name="CUST_PHONE",
072 *        joinColumns=
073 *            &#064;JoinColumn(name="CUST_ID", referencedColumnName="ID"),
074 *        inverseJoinColumns=
075 *            &#064;JoinColumn(name="PHONE_ID", referencedColumnName="ID")
076 *        )
077 *    Set&#060;PhoneNumber&#062; phones;
078 *
079 *    // In PhoneNumberClass:
080 *
081 *    &#064;ManyToMany(mappedBy="phones")
082 *    Set&#060;Customer&#062; customers;
083 * </pre>
084 *
085 * @see JoinTable
086 * @since Java Persistence 1.0
087 */
088@Target({FIELD})
089@Retention(RUNTIME)
090public @interface ManyToMany {
091
092  /**
093   * (Optional) The entity class that is the target of the association. Optional only if the
094   * collection-valued relationship property is defined using Java generics. Must be specified otherwise.
095   * <p>
096   * Defaults to the parameterized type of the collection when defined using generics.
097   *
098   * @return The target entity
099   */
100  Class targetEntity() default void.class;
101
102  /**
103   * (Optional) The operations that must be cascaded to the target of the association.
104   * <p>
105   * When the target collection is a {@link java.util.Map java.util.Map}, the <code>cascade</code> element
106   * applies to the map value.
107   * <p>
108   * Defaults to no operations being cascaded.
109   *
110   * @return The cascade type
111   */
112  CascadeType[] cascade() default {};
113
114  /**
115   * (Optional) Whether the association should be lazily loaded or must be eagerly fetched. The EAGER
116   * strategy is a requirement on the persistence provider runtime that the associated entities must be
117   * eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.
118   *
119   * @return The fetch type
120   */
121  FetchType fetch() default LAZY;
122
123  /**
124   * The field that owns the relationship. Required unless the relationship is unidirectional.
125   *
126   * @return The mappedby
127   */
128  String mappedBy() default "";
129}