protected function _findExistingTranslations($ruleSet)
    {
        $association = $this->_table->getAssociation($this->_translationTable->getAlias());

        $query = $association->find()
            ->select(['id', 'num' => 0])
            ->where(current($ruleSet))
            ->disableHydration()
            ->disableBufferedResults();

        unset($ruleSet[0]);
        foreach ($ruleSet as $i => $conditions) {
            $q = $association->find()
                ->select(['id', 'num' => $i])
                ->where($conditions);
            $query->unionAll($q);
        }

        return $query->all()->combine('num', 'id')->toArray();
    }