public function prepareSave($parentRow, $postData)
 {
     $row = $this->_getRowByParentRow($parentRow);
     if (!$row) {
         throw new Kwf_Exception('Can\'t find row.');
     } else {
         if (!$row instanceof Kwf_Model_Row_Interface) {
             throw new Kwf_Exception('Row must be a Kwf_Model_Row_Interface.');
         }
     }
     parent::prepareSave($parentRow, $postData);
 }