public int Update(string collection, IEnumerable <BsonDocument> docs)
 {
     try
     {
         NotificationService.Cache.AddDocuments(collection, docs);
         var result = _engine.Update(collection, docs);
         NotificationService.Notify();
         return(result);
     }
     catch (Exception ex)
     {
         throw ex;
     }
     finally
     {
         NotificationService.Clear();
     }
 }