code: protected function getResultSetKey($query, $limit, $offset, $orderBy, $facets)
      {
          $facetsParams = array();
          foreach ($facets as $facet) {
              $facetsParams[] = $facet->getParams();
          }
  
          return md5(
              var_export($query->toArray(), true).$limit.$offset.var_export($orderBy, true).var_export($facetsParams, true)
          );
      }
docs: @param $query
  @param $limit
  @param $offset
  @param $orderBy
  @param $facets
  
  @return string