/**
  * saves the form fields to the database
  * 
  * @param ilPropertyFormGUI $form
  * @return boolean
  */
 private function performSaveForm(ilPropertyFormGUI $form)
 {
     $this->questionSetConfig->setSourceQuestionPoolId($form->getItemByPostVar('source_qpl_id')->getValue());
     $this->questionSetConfig->setSourceQuestionPoolTitle(ilObject::_lookupTitle($form->getItemByPostVar('source_qpl_id')->getValue()));
     switch ($form->getItemByPostVar('question_ordering')->getValue()) {
         case self::QUESTION_ORDERING_TYPE_UPDATE_DATE:
             $this->questionSetConfig->setOrderingTaxonomyId(null);
             break;
         case self::QUESTION_ORDERING_TYPE_TAXONOMY:
             $this->questionSetConfig->setOrderingTaxonomyId($form->getItemByPostVar('ordering_tax')->getValue());
             break;
     }
     $this->questionSetConfig->setTaxonomyFilterEnabled($form->getItemByPostVar('tax_filter_enabled')->getChecked());
     return $this->questionSetConfig->saveToDb($this->testOBJ->getTestId());
 }