function getSelectedColumns()
 {
     $scol = parent::getSelectedColumns();
     $cols = $this->getSelectableColumns();
     if (!is_array($cols)) {
         $cols = array();
     }
     $fields_to_unset = array_diff(array_keys($scol), array_keys($cols));
     foreach ($fields_to_unset as $key) {
         unset($scol[$key]);
     }
     return $scol;
 }