/**
  *
  */
 public function getCaptionFileInstance($pn_caption_id)
 {
     if (!$this->getPrimaryKey()) {
         return null;
     }
     $t_caption = new ca_object_representation_captions($pn_caption_id);
     if ($this->inTransaction()) {
         $t_caption->setTransaction($this->getTransaction());
     }
     if ($t_caption->get('representation_id') == $this->getPrimaryKey()) {
         return $t_caption;
     }
     return null;
 }