Base query for an url and xpath

        Args:
            url (str): URL to search
            xpath (str): xpath to search (may be ``None``)

def _query(self, url, xpath):
        """Base query for an url and xpath

        Args:
            url (str): URL to search
            xpath (str): xpath to search (may be ``None``)
        """
        return self.session.query(CachedRequest).filter(CachedRequest.url == url).filter(CachedRequest.xpath == xpath)