protected function _hasRefsIn($key, $filter, $options, $ttl = 0) {
		$type = $this->fieldConf[$key]['relType'];
		$fieldConf = $this->fieldConf[$key][$type];
		// one-to-many shortcut
		$rel = $this->getRelFromConf($fieldConf,$key);
		$hasSet = $rel->find($filter, $options, $ttl);
		if (!$hasSet)
			return false;
		$hasSetByRelId = array_unique($hasSet->getAll($fieldConf[1], true));
		return empty($hasSetByRelId) ? false : $hasSetByRelId;
	}