public function associated_files_path()
 {
     static $cache;
     if (!isset($cache[$this->object_name])) {
         $instance_name = Database::instance_name($this->db);
         $directory = Kohana::config('orm_files.' . $instance_name, TRUE, TRUE);
         $cache[$this->object_name] = $directory . $this->db->table_prefix() . $this->table_name . '/';
     }
     return $cache[$this->object_name];
 }