partial void DeleteLetter(Letter instance);
 partial void UpdateLetter(Letter instance);
 private void detach_Letters(Letter entity)
 {
     this.SendPropertyChanging();
     entity.Check = null;
 }
 partial void InsertLetter(Letter instance);
 private void attach_Letters(Letter entity)
 {
     this.SendPropertyChanging();
     entity.Check = this;
 }