def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def __init__(self, schema_file: str):
        self._schema = artifact_utils.read_schema_file(schema_file)

        self._type_name, self._metric_fields = artifact_utils.parse_schema(
            self._schema)

        self._values = {}