notification method

Implementation

@override
void notification(TComponent aComponent, TOperation operation) {
  super.notification(aComponent, operation);
  if (operation == TOperation.opRemove) {
    if (identical(aComponent, _transaction)) {
      _transaction = null;
    } else if (identical(aComponent, _database)) {
      unprepare();
      _database = null;
    }
  }
}