511 words

javax.persistence.ManyToOne - JPA annotation

javax.persistence
Annotation ManyToOne

Target:
Fields (including property get methods)
Defines a single-valued association to another entity class that has many-to-one multiplicity. It is not normally necessary to specify the target entity explicitly since it can usually be inferred from the type of the object being referenced. If the relationship is bidirectional, the non-owning OneToMany entity side must used the mappedBy element to specify the relationship field or property of the entity that is the owner of the relationship.

The ManyToOne annotation may be used within an embeddable class to specify a relationship from the embeddable class to an entity class. If the relationship is bidirectional, the non-owning OneToMany entity side must use the mappedBy element of the OneToMany annotation to specify the relationship field or property of the embeddable field or property on the owning side of the relationship. 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:

     @ManyToOne(optional=false) 
     @JoinColumn(name="CUST_ID", nullable=false, updatable=false)
     public Customer getCustomer() { return customer; }

Example 2:

 
     @Entity
        public class Employee {
        @Id int id;
        @Embedded JobInfo jobInfo;
        ...
     }
 
     @Embeddable
        public class JobInfo {
        String jobDescription; 
        @ManyToOne ProgramManager pm; // Bidirectional
     }
 
     @Entity
        public class ProgramManager {
        @Id int id;
        @OneToMany(mappedBy="jobInfo.pm")
        Collection<Employee> manages;
     }

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.

By default no operations are cascaded.

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 entity must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.
Default value:
javax.persistence.FetchType.EAGER
Since:
JPA 1.0
boolean optional
(Optional) Whether the association is optional.
(Optional) Whether the association is optional. If set to false then a non-null relationship must always exist.
Default value:
true
Since:
JPA 1.0
(Optional) The entity class that is the target of the association.
(Optional) The entity class that is the target of the association.

Defaults to the type of the field or property that stores the association.

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.