function read_single($id)
 {
     $document = parent::read_single($id);
     if (is_array($document)) {
         $document['filename'] = $this->generate_filename($document['id'], $document['name']);
     }
     return $document;
 }
 function read_single($id)
 {
     $entity = parent::read_single($id);
     $this->initialize_entity($entity);
     return $entity;
 }