def get_next_id(self):
        try:
            query = {'_id': 'last_id'}
            update = {'$inc': {'id': 1}}
            fn = self.db.internal.find_and_modify
            row = fn(query, update, upsert=True, new=True)
        except Exception as e:
            raise DatabaseException(e)
        return row['id']
def _split(self, path):
        if "/" in path:
            subdir, rest = path.split("/", 1)
        else:
            subdir, rest = path, ""
        if not subdir:
            raise error.ProgrammingError("path cannot be absolute")
        return subdir, rest