OneToOne Class
NPersistence Reference Guide
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.

Examples

CopyC#
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;
    ... 
}

Namespace: NPersistence
Assembly: NPersistence (in NPersistence.dll) Version: 2.0.0.0 (2.0.0.0)

Syntax

   
 C# 
public sealed class OneToOne : Attribute

Members

         
 All Members  Constructors   Fields  
 Public

 Protected
 Instance

 Static 
 Declared

 Inherited
 XNA Framework Only 

 .NET Compact Framework Only 

 MemberDescription
OneToOne()()()()
Initializes a new instance of the OneToOne class
Cascade
(Optional) The operations that must be cascaded to the target of the association. By default no operations are cascaded.
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.
MappedBy
(Optional) The field that owns the relationship. This element is only specified on the inverse (non-owning) side of the association.
Optional
(Optional) Whether the association is optional. If set to false then a non-null relationship must always exist.
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.
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.

Inheritance Hierarchy

System..::..Object
  System..::..Attribute
    NPersistence..::..OneToOne

See Also