code: protected function getMatchingIds($objFilter)
      {
          if ($objFilter) {
              $arrFilteredIds = $objFilter->getMatchingIds();
              if ($arrFilteredIds !== null) {
                  return $arrFilteredIds;
              }
          }
  
          // Either no filter object or all ids allowed => return all ids.
          // if no id filter is passed, we assume all ids are provided.
          return $this->getConnection()->createQueryBuilder()
              ->select('id')
              ->from($this->getTableName())
              ->execute()
              ->fetchAll(\PDO::FETCH_COLUMN);
      }
docs: Narrow down the list of Ids that match the given filter.
  
  @param IFilter|null $objFilter The filter to search the matching ids for.
  
  @return array all matching Ids.