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 deserialize(self, value):
        value = decode(value)
        validators.validate_required(value, self._required)
        if not value:
            return None
        value = int(value)
        validators.validate_choice(value, self._choices)
        validators.validate_minimum(value, self._minimum)
        validators.validate_maximum(value, self._maximum)
        return value