javax.persistence

Annotation Type OneToOne

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

This annotation 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.

    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 @PrimaryKeyJoinColumn
        EmployeeInfo info;
        ...
    }

    On EmployeeInfo class:

    @Entity
    public class EmployeeInfo {
        @Id Integer id;
        ...
    }
 

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.
String	mappedBy (Optional) The field that owns the relationship.
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

mappedBy

public abstract String mappedBy

(Optional) The field that owns the relationship. This element is only specified on the inverse (non-owning) side of the association.

Default:

""