javax.persistence

Annotation Type ManyToOne

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

Specifies 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:

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.
boolean	optional (Optional) Whether the association is optional.
Class	targetEntity (Optional) The entity class that is the target of the association.

Element Detail

targetEntity

public abstract Class targetEntity

(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:

void.class

cascade

public abstract CascadeType[] cascade

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

By default no operations are 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 entity must be eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.

Default:

javax.persistence.FetchType.EAGER

optional

public abstract boolean optional

(Optional) Whether the association is optional. If set to false then a non-null relationship must always exist.

Default:

true