/**
  * Return a query for the requested objects.
  * @param string $object_type
  * @return QUERY
  * @access private
  */
 protected function _object_query_for($object_type)
 {
     switch ($object_type) {
         case History_item_branch:
             return $this->login->all_branch_query();
         case History_item_release:
             return $this->login->all_release_query();
         case History_item_component:
             return $this->login->all_release_query();
         default:
             return parent::_object_query_for($object_type);
     }
 }