update method
update modified fields within callback by key(s),
Implementation
Future<RowData?> update(VoidCallback callback, {SQLExecutor? executor}) async {
_modifiedKeys.clear();
callback();
if (_modifiedKeys.isEmpty) return null;
_modifiedKeys.clear();
var ls = _modifiedKeys.toList();
return await updateByKey(columns: ls, executor: executor);
}