Append tags to tag list. Don't add same tag more than once.

def tag_alert(self, id, tags):
        """
        Append tags to tag list. Don't add same tag more than once.
        """
        response = self.get_db().alerts.update_one(
            {'_id': {'$regex': '^' + id}}, {'$addToSet': {'tags': {'$each': tags}}})
        return response.matched_count > 0