protected function _refSubQuery($key, $filter, $options,$fields=null) {
		$type = $this->fieldConf[$key]['relType'];
		$fieldConf = $this->fieldConf[$key][$type];
		$rel = $this->getRelFromConf($fieldConf,$key);
		$filter[0]=$this->queryParser->sql_quoteCondition($filter[0],$this->db);
		return $rel->mapper->stringify(implode(',',array_map([$this->db,'quotekey'],
			$fields?:[$rel->primary])),$filter,$options);
	}