def get_metadata_by_userid(self, userid):
        """get metadata record.
        output should be like: "a=1,b=2,c=3"
        """
        userid = userid
        with get_guest_conn() as conn:
            res = conn.execute("SELECT * FROM guests "
                               "WHERE userid=?", (userid,))
            guest = res.fetchall()

        if len(guest) == 1:
            return guest[0][2]
        elif len(guest) == 0:
            LOG.debug("Guest with userid: %s not found from DB!" % userid)
            return ''
        else:
            msg = "Guest with userid: %s have multiple records!" % userid
            LOG.error(msg)
            raise exception.SDKInternalError(msg=msg, modID=self._module_id)
get metadata record.
        output should be like: "a=1,b=2,c=3"