Home » JPA » Annotations » Relationships » OneToOne
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javax.persistence.OneToOne - JPA annotation

javax.persistence
Annotation OneToOne

Target:
Fields (including property get methods)
When using ObjectDB - this annotation is optional.
Defines a single-valued association to another entity that has one-to-one multiplicity. It is not normally 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 mappedBy element of the OneToOne annotation to specify the relationship field or property of the owning side.

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 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 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

    // On Customer class:
 
    @OneToOne(optional=false)
    @JoinColumn(
      name="CUSTREC_ID", unique=true, nullable=false, updatable=false)
    public CustomerRecord getCustomerRecord() { return customerRecord; }
 
    // On CustomerRecord class:
 
    @OneToOne(optional=false, mappedBy="customerRecord")
    public Customer getCustomer() { return customer; }

Example 2: One-to-one association that assumes both the source and target share the same primary key values. 

    // On Employee class:
 
    @Entity
    public class Employee {
      @Id Integer id;
 
      @OneToOne @MapsId
      EmployeeInfo info;
      ...
    }
 
    // On EmployeeInfo class:
 
    @Entity
    public class EmployeeInfo {
      @Id Integer id;
      ...
    }

Example 3: One-to-one association from an embeddable class to another entity.

    @Entity
    public class Employee {
       @Id int id;
       @Embedded LocationDetails location;
       ...
    }
 
    @Embeddable
    public class LocationDetails {
       int officeNumber;
       @OneToOne ParkingSpot parkingSpot;
       ...
    }
 
    @Entity
    public class ParkingSpot {
       @Id int id;
       String garage;
       @OneToOne(mappedBy="location.parkingSpot") Employee assignedTo;
        ... 
    }

Since:
JPA 1.0
Post comment by ObjectDB
CascadeType[] cascade
(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
FetchType fetch
(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
String mappedBy
(Optional) The field that owns the relationship.
(Optional) The field that owns the relationship. This element is only specified on the inverse (non-owning) side of the association.
Default value:
""
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
boolean orphanRemoval
(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
Class targetEntity
(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.