protected override void OnAbortTransaction()
 {
     if (_instance == this)
     {
         _instance = null;
     }
 }
 protected override void OnCompleteTransaction()
 {
     if (_instance == this)
     {
         _instance = null;
     }
 }
 protected override void OnBeginTransaction()
 {
     if (_instance == null)
     {
         _instance = this;
     }
 }