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, config_d, path=None, resolver=None):
        super().__init__(path=path, resolver=resolver)
        self._collection = {}
        for key, value in config_d.items():
            self._collection[key] = self._from_python(key, value)