/**
  * 
  */
 function getFilename()
 {
     if (empty($this->filename)) {
         $wa = new PHPWikiAttachment();
         // @todo: catch error when wiki no attachementId is set.
         $wa->initWithId($this->attachmentId);
         // @todo: catch error when given attchId do not exist
         $this->displayFilename = $wa->getFilename();
         $this->filename = $wa->getFilesystemName();
     }
     return $this->filename;
 }