543 words

javax.persistence.OneToMany - JPA annotation

javax.persistence
Annotation OneToMany

Target:
Fields (including property get methods)
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. If the relationship is bidirectional, the mappedBy element must be used to specify the relationship field or property of the entity that is the owner of the relationship.

The OneToMany 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, the mappedBy element must be used to specify the relationship field or property of the entity that is the owner of the relationship. When the collection is a java.util.Map, the cascade element and the orphanRemoval element apply to the map value.

Example 1: One-to-Many association using generics

    // In Customer class:
 
    @OneToMany(cascade=ALL, mappedBy="customer")
    public Set<Order> 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; }

Example 3: Unidirectional One-to-Many association using a foreign key mapping

    // In Customer class:
 
    @OneToMany(orphanRemoval=true)
    @JoinColumn(name="CUST_ID") // join column is in table for Order
    public Set<Order> getOrders() {return orders;}

Since:
JPA 1.0
(Optional) The operations that must be cascaded to the target of the association.
(Optional) The operations that must be cascaded to the target of the association.

Defaults to no operations being cascaded.

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

Default value:
{}
Since:
JPA 1.0
(Optional) Whether the association should be lazily loaded or must be eagerly fetched.
(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 value:
javax.persistence.FetchType.LAZY
Since:
JPA 1.0
String mappedBy
The field that owns the relationship.
The field that owns the relationship. Required unless the relationship is unidirectional.
Default value:
""
Since:
JPA 1.0
(Optional) Whether to apply the remove operation to entities that have been removed from the relationship and to cascade the remove operation to those entities.
(Optional) Whether to apply the remove operation to entities that have been removed from the relationship and to cascade the remove operation to those entities.
Default value:
false
Since:
JPA 2.0
(Optional) The entity class that is the target of the association.
(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.

Default value:
void.class
Since:
JPA 1.0

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
Object DB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.