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 image_url(self, name, override_receipt_id=None):
        """
        We dynamically generate this, since we want it the expiration clock to
        start when the message is created, not when the record is created.

        Arguments:
            name (str): Name of the image (e.g. "photo_id" or "face")

        Keyword Arguments:
            override_receipt_id (str): If provided, use this receipt ID instead
                of the ID for this attempt.  This is useful for reverification
                where we need to construct a URL to a previously-submitted
                photo ID image.

        Returns:
            string: The expiring URL for the image.

        """
        path = self._get_path(name, override_receipt_id=override_receipt_id)
        return self._storage.url(path)