public void UpdateVisitor (Visitor visitor)
		{
			if (IsQueryPossible) {
				_connection.Transaction (() => _connection.InsertOrReplace (visitor));
			}
		}
		public void DeleteVisitor (Visitor visitor)
		{
			if (IsQueryPossible) {
				_connection.Transaction (() => _connection.Delete (visitor));
			}
		}
		public void InsertVisitor (Visitor visitor)
		{
			if (IsQueryPossible) {
				_connection.Transaction (() => _connection.Insert (visitor));
			}
		}