docs: 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)