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 update(self, *args, **kwargs):
        chain = []
        for arg in args:
            if isinstance(arg, dict):
                iterator = arg.items()
            else:
                iterator = arg
            chain = itertools.chain(chain, iterator)
        if kwargs:
            chain = itertools.chain(chain, kwargs.items())
        for key, value in iterator:
            self._collection[key] = self._from_python(key, value)