session中类对象的保存

好象需要序列化之后才能保存，
取得时候再反序列化还原

如果不这样的话，出现 [instance of __PHP_Incomplete_Class given]错误？

                $cond = new Search_Cond_Tour();
                if ($cond_to_session) {
                        $cond->_customer_type = $_POST['customer_type'];
                        $cond->_tour_type = $_POST['tour_type'];
                        $cond->_public_flag =  $_POST['public_flag'];
                        $this->session->set_userdata('search_tour_cond',serialize($cond));
                } else {
                        $cond= unserialize($this->session->userdata('search_tour_cond'))；
                }