$reader = new XMLReader();
         $reader->open('update_xml/SiteData2.xml');

         while ($reader->read()) {
             if ($reader->name == "Apartment") {
               //  echo '<p>'.$reader->getAttribute("kvnumber").'</p>';


                  $building_id = (int)$reader->getAttribute("buildingid");
                  $apartment_id = (int)$reader->getAttribute("id");
              

                   $rooms = $reader->getAttribute("rooms");
                   $flatfloor = $reader->getAttribute("flatfloor");
                   $facing = $reader->getAttribute("decoration");

              $sql3 = "SELECT sub_object_id FROM `#__sub_objects` 
                       WHERE `apartment_id` = '$apartment_id'";
              $db->setQuery($sql3);
              $sub_object_id = $db->loadResult();    

              $sql3 = "SELECT sub_object_id,apartment_id FROM `#__sub_objects`";
              $db->setQuery($sql3);
              $this->sub_objects = $db->loadAssocList();   

$sub_object_id = $this->search_sub_object_id($apartment_id); 

function search_sub_object_id($val){
      
               foreach ($this->sub_objects as $key => $value)
                   {
                   if (array_search ($val, $value))
                        {
                        return ($value['sub_object_id']);
                        }   
                   }
}