OneToMany (Java EE 5 SDK)

javax.persistence Annotation Type OneToMany

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

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.

    Example 1: One-to-Many association using generics

    In Customer class:

    @OneToMany(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 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; }
 

从以下版本开始:

Java Persistence 1.0

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.

默认值:

LAZY

mappedBy

public abstract String mappedBy

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

默认值:

""

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