protected function fetchExistingIdsFor($idList, $langCode)
    {
        $queryBuilder = $this
            ->connection
            ->createQueryBuilder()
            ->select('item_id')
            ->from($this->getValueTable());
        $this->buildWhere($queryBuilder, $idList, $langCode);

        $statement = $queryBuilder->execute();

        return $statement->fetchAll(\PDO::FETCH_COLUMN);
    }