private bool FilterChildren(NullableFKChild entity)
 {
     return (entity.ParentID == this.ID);
 }
 private void AttachChildren(NullableFKChild entity)
 {
     entity.Parent = this;
 }
 private void DetachChildren(NullableFKChild entity)
 {
     entity.Parent = null;
 }
 private bool FilterChild(NullableFKChild entity)
 {
     return (entity.ParentID_Singleton == this.ID);
 }