Annotation Interface ManyToMany

@Target({METHOD,FIELD}) @Retention(RUNTIME) public @interface ManyToMany
Specifies a many-valued association with many-to-many multiplicity, mapping to an intermediate table called the join table. If the target entity class cannot be inferred from the type arguments of the declared type of the annotated field or property, then targetEntity() must be explicitly specified.

The optional JoinTable annotation specifies the mapped join table. 

@ManyToMany
@JoinTable(name = "BOOK_AUTHOR",
           joinColumns = @JoinColumn(name = "BOOK_ISBN",
                                     referencedColumnName = "ISBN"),
           inverseJoinColumns = @JoinColumn(name = "AUTHOR_SSN",
                                            referencedColumnName = "SSN"))
Set<Author> authors;

The annotated field or property might represent one side of a bidirectional association. Every bidirectional association has an owning side and an inverse (alternatively, non-owning or unowned) side. Modifications to the owning side of an association determine the updates made to the relationship in the database. If the inverse side of an association is modified without a corresponding modification to the owning side, the behavior is undefined. The persistence provider is permitted to ignore any modification made only to the inverse side of a bidirectional association.

The inverse side of a bidirectional ManyToMany association must be a field or property also annotated @ManyToMany of the target entity, and the inverse side must specify the owning relationship field or property via mappedBy(). The join table must be specified on the owning side. 

@Entity
public class Book {
    @Id
    String isbn;

    // owning side
    @ManyToMany
    @JoinTable(name = "BOOK_AUTHOR")
    Set<Author> authors;
    ...
}

@Entity
public class Author {
    @Id
    String ssn;

    // inverse (unowned) side
    @ManyToMany(mappedBy = Book_.AUTHORS)
    Set<Customer> customers;
    ...
}

The ManyToMany 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 and the entity containing the embeddable class is the owner of the relationship, the non-owning side must use the mappedBy() element of the ManyToMany annotation to specify the relationship field or property of the embeddable class. The dot (.) notation syntax must be used in the mappedBy() element to indicate the relationship attribute within the embedded attribute. The value of each identifier used with the dot notation is the name of the respective embedded field or property.

Since:
1.0
See Also:

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    CascadeType[]
    cascade
    (Optional) The operations that must be cascaded to the target of the association.
    FetchType
    fetch
    (Optional) Whether the association should be lazily loaded or must be eagerly fetched.
    String
    mappedBy
    The field or property of the target entity that owns the relationship and specifies its mapping to the database.
    Class<?>
    targetEntity
    (Optional) The entity class that is the target of the association.

  • Element Details

    • targetEntity

      Class<?> targetEntity
      (Optional) The entity class that is the target of the association. Required if the target entity type cannot be inferred from the declared type of the annotated field or property, for example, if the declared type is a raw collection type.

      Defaults to the type argument of the collection type when the declared type of the annotated field or property is a non-raw collection type.

      Default:
      void.class

    • cascade

      CascadeType[] cascade
      (Optional) The operations that must be cascaded to the target of the association.

      When the target collection is a Map, the cascade element applies to the map value.

      By default, no operations are cascaded.

      Default:
      {}

    • fetch

      FetchType fetch
      (Optional) Whether the association should be lazily loaded or must be eagerly fetched.
      • The EAGER policy is a requirement on the persistence provider runtime that the associated entity must be eagerly fetched.
      • The LAZY policy is a hint to the persistence provider runtime.

      If not specified, defaults to LAZY.

      Default:
      LAZY

    • mappedBy

      String mappedBy
      The field or property of the target entity that owns the relationship and specifies its mapping to the database. This element is only specified on the inverse (non-owning) side of the association.

      The static metamodel of the target entity may be used to obtain a reference to the owning side, for example, mappedBy = Book_.AUTHORS.

      Default:
      ""