snapshot method
Implementation
@override
Future<void> snapshot(FieldData fieldData, int ts, int user_ts) async {
if (!initialized) throw ArgumentError(AbstractDao.C_MUST_INIT);
TrDto trDto = TrDto.sep(ts, OperationType.SNAPSHOT, 0, user_ts,
"Configuration Snapshot", null, ConfigurationMixin.C_TABLE_ID,
fieldData: fieldData);
await configurationTrDao.setConfigurationTrDto(trDto as ConfigurationTrDto);
}