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 update_snapshot_metadata_item(self, snapshot_id, id, meta_item):
        """Update metadata item for the snapshot."""
        put_body = json.dumps({'meta': meta_item})
        url = "snapshots/%s/metadata/%s" % (str(snapshot_id), str(id))
        resp, body = self.put(url, put_body)
        body = json.loads(body)
        return resp, body['meta']