function find_by_title($title)
 {
     $c_id = $this->c_id;
     $session_id = $this->session_id;
     $repo = CourseDescriptionRepository::instance();
     $link = $repo->find_one_by_course_and_title($c_id, $session_id, $title);
     return $link;
 }
 /**
  * Return the repository.
  *
  * @return \CourseDescription\CourseDescriptionRepository
  */
 public static function repository()
 {
     return CourseDescriptionRepository::instance();
 }