private void detach_HoaDons(HoaDon entity)
 {
     this.SendPropertyChanging();
     entity.Tua = null;
 }
 private void attach_HoaDons(HoaDon entity)
 {
     this.SendPropertyChanging();
     entity.Tua = this;
 }
 partial void UpdateHoaDon(HoaDon instance);
 partial void DeleteHoaDon(HoaDon instance);
 partial void InsertHoaDon(HoaDon instance);