public function deleteSelect()
 {
     // All methods inside this controller are only accessible for admins (= users that have role type 7)
     Auth::checkAdminAuthentication();
     $idArray = $_POST['check_list'];
     foreach ($idArray as $material_id) {
         MaterialModel::deleteMaterial($material_id);
     }
     Redirect::to('material/index/0');
 }