ManyToMany (Java EE 5 SDK)

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Java EE 5 SDK

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摘要: REQUIRED | OPTIONAL

详细信息: ELEMENT

javax.persistence Annotation Type ManyToMany

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

Defines a many-valued association with many-to-many multiplicity. If the Collection is defined using generics to specify the element type, the associated target entity class does not need to be specified; otherwise it must be specified.

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.

The same annotation elements for the OneToMany annotation apply to the ManyToMany annotation.


    Example 1:

    In Customer class:

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

    In PhoneNumber class:

    @ManyToMany(mappedBy="phones")
    public Set 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 getPhones() { return phones; }

    In PhoneNumberClass:

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

从以下版本开始:: Java Persistence 1.0

Optional Element Summary
`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 that owns the relationship.
`Class`	`targetEntity` (Optional) The entity class that is the target of the association.

targetEntity

public abstract Class targetEntity

(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.

默认值:: void.class

cascade

public abstract CascadeType[] cascade

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

Defaults to no operations being cascaded.

默认值:: {}

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 persistenceprovider runtime that the associatedentities must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.