def _set_named_args(self, **kv):
        """
        Set a named parameter in the query. The named field must
        exist in the query itself.

        :param kv: Key-Value pairs representing values within the
            query. These values should be stripped of their leading
            `$` identifier.

        """
        for k in kv:
            self._body['${0}'.format(k)] = kv[k]
        return self