code: 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);
      }
docs: Filter the item ids for ids that exist in the database.
  
  @param array  $idList   The id list.
  @param string $langCode The language code.
  
  @return string[]