Module persistence.api
Package javax.persistence

Annotation Type ManyToOne

@Target(FIELD) @Retention(RUNTIME) public @interface ManyToOne
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)
     Customer 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
    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 Details

    • targetEntity

      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.

      Returns:
      The target entity
      Default:
      void.class

    • cascade

      CascadeType[] cascade
      (Optional) The operations that must be cascaded to the target of the association.

      By default no operations are cascaded.

      Returns:
      The cascade type
      Default:
      {}

    • fetch

      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.
      Returns:
      The fetch type
      Default:
      EAGER

    • optional

      boolean optional
      (Optional) Whether the association is optional. If set to false then a non-null relationship must always exist.
      Returns:
      Whether this is optional
      Default:
      true