Example of one-to-one-association implementation

Hi,

could you please provide me with an example of a lightspeed-implementation of a one-to-one association?

Thank you,
Henning

  public sealed class Car : Entity<int>
  {
    private string _registration;

    internal readonly EntityHolder<Engine> _engine
      = new EntityHolder<Engine>();

    public string Registration
    {
      get { return Get(ref _registration); }
      set { Set(ref _registration, value); }
    }

    public Engine Engine
    {
      get { return Get(_engine); }
      set { Set(_engine, value); }
    }
  }

  public sealed class Engine : Entity<int>
  {
    private string _manufacturersReference;

    private int? _carId;

    private readonly EntityHolder<Car> _car
      = new EntityHolder<Car>();

    public string ManufacturersReference
    {
      get { return Get(ref _manufacturersReference); }
      set { Set(ref _manufacturersReference, value); }
    }

    public int? CarId
    {
      get { return Get(ref _carId); }
      set { Set(ref _carId, value); }
    }

    public Car Car
    {
      get { return Get(_car); }
      set { Set(_car, value); }
    }
  }