javax.persistence

Annotation Type ManyToMany

@Target(value={METHOD,FIELD})
@Retention(value=RUNTIME)
public @interface ManyToMany

Specifies a many-valued association with many-to-many multiplicity.

Every many-to-many association has two sides, the owning side and the non-owning, or inverse, side. The join table is specified on the owning side. If the association is bidirectional, either side may be designated as the owning side. If the relationship is bidirectional, the non-owning side must use the mappedBy element of the ManyToMany annotation to specify the relationship field or property of the owning side.

The join table for the relationship, if not defaulted, is specified on the owning side.

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.

    Example 1:

    // In Customer class:

    @ManyToMany
    @JoinTable(name="CUST_PHONES")
    public Set<PhoneNumber> getPhones() { return phones; }

    // In PhoneNumber class:

    @ManyToMany(mappedBy="phones")
    public Set<Customer> getCustomers() { return customers; }

    Example 2:

    // In Customer class:

    @ManyToMany(targetEntity=com.acme.PhoneNumber.class)
    public Set getPhones() { return phones; }

    // In PhoneNumber class:

    @ManyToMany(targetEntity=com.acme.Customer.class, mappedBy="phones")
    public Set getCustomers() { return customers; }

    Example 3:

    // In Customer class:

    @ManyToMany
    @JoinTable(name="CUST_PHONE",
        joinColumns=
            @JoinColumn(name="CUST_ID", referencedColumnName="ID"),
        inverseJoinColumns=
            @JoinColumn(name="PHONE_ID", referencedColumnName="ID")
        )
    public Set<PhoneNumber> getPhones() { return phones; }

    // In PhoneNumberClass:

    @ManyToMany(mappedBy="phones")
    public Set<Customer> getCustomers() { return customers; }
 

See Also:

JoinTable

Since:

Java Persistence 1.0

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and 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.
java.lang.String	mappedBy The field that owns the relationship.
java.lang.Class	targetEntity (Optional) The entity class that is the target of the association.

Element Detail

targetEntity

public abstract java.lang.Class targetEntity

(Optional) The entity class that is the target of the association. Optional only if the collection-valued relationship property is defined using Java generics. Must be specified otherwise.

Defaults to the parameterized type of the collection when defined using generics.

Default:

void.class

cascade

public abstract CascadeType[] cascade

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

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

Defaults to no operations being cascaded.

Default:

{}

fetch

public abstract FetchType fetch

(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.

Default:

javax.persistence.FetchType.LAZY

mappedBy

public abstract java.lang.String mappedBy

The field that owns the relationship. Required unless the relationship is unidirectional.

Default:

""