ecstore中怎样使用ajax提交数据

    //javascript代码
    $$(".bb").addEvent('change',function(e){
       var order_item_id =  this.get('order_item_id');
       var product_name= this.value;
       new Request.JSON({
            url: "index.PHP?app=sale&ctl=admin_orders&act=ajax_discount", 
            onComplete: function(person, text){
                if(person.status==1){
                    alert(person.msg);
                }else{
                    alert("提交失败");
                }
            }
        }).post('order_item_id='+order_item_id+'&product_name='+product_name);
    });
    //后台方法
    function ajax_discount(){
        $id = $_POST['order_item_id'];
        $product_name =  $_POST['product_name]
        $order_item_mdl = $this->app->model('orders_item');
        $order_item = $order_item_mdl->dump($id);
        $order_item['product_name']=$product_name;
        $order_item_mdl->save($order_item);
        $result = array('status'=>1,'msg'='信息修改成功']);
        echo json_encode($result);
    }