JPA Annotation

OneToOne

Target: METHOD, FIELD
Implemented Interfaces:
Annotation
Specifies a single-valued association to another entity class that has one-to-one multiplicity. It is not usually necessary to specify the associated 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 side must use the OneToOne.mappedBy element of the OneToOne annotation to specify the relationship field or property of the owning side.

A OneToOne association usually maps a unique foreign key relationship, either a foreign key column or columns with a unique constraint, or a relationship via a shared primary key. The JoinColumn annotation may be used to map the foreign key column or columns. Alternatively, an optional OneToOne association is sometimes mapped to a join table using the JoinTable annotation.

The OneToOne 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 and the entity containing the embeddable class is on the owning side of the relationship, the non-owning side must use the OneToOne.mappedBy element of the OneToOne annotation to specify the relationship field or property of the embeddable class. The dot (.) notation syntax must be used in the OneToOne.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:

 One-to-one association that maps a foreign key column
 {@snippet :
 // On Customer class:
Since:
JPA 1.0

Public Annotation Attributes

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

By default no operations are cascaded.

Since:
JPA 1.0
FetchType fetch default FetchType.EAGER
(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.

If not specified, defaults to EAGER.

Since:
JPA 1.0
String mappedBy default ""
(Optional) The field that owns the relationship.
This element is only specified on the inverse (non-owning) side of the association.
Since:
JPA 1.0
boolean optional default true
(Optional) Whether the association is optional.
If set to false then a non-null relationship must always exist.
Since:
JPA 1.0
boolean orphanRemoval default false
(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.
Since:
JPA 2.0
Class<?> targetEntity default void.class
(Optional) The entity class that is the target of the association.

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

Since:
JPA 1.0