/**
  * Return an index name based on artifact link field id
  *
  * @param Tracker_FormElementFactory $form_element_factory
  *
  * @return String
  */
 public function getArtifactLinkFieldName(Tracker_FormElementFactory $form_element_factory)
 {
     $fields = $form_element_factory->getUsedArtifactLinkFields($this->getTracker());
     if (empty($fields)) {
         return;
     }
     return 'art_link_' . $fields[0]->getId();
 }