@Target(value={METHOD,FIELD}) @Retention(value=RUNTIME) public @interface OneToOne
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;
        ... 
    } 
 | 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. | 
| 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. | 
| Class | targetEntity(Optional) The entity class that is the target of 
 the association. | 
public abstract Class targetEntity
Defaults to the type of the field or property that stores the association.
public abstract CascadeType[] cascade
By default no operations are cascaded.
public abstract FetchType fetch
public abstract boolean optional
public abstract String mappedBy
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