iwebshop模拟秒杀

//秒杀模拟练习
public function sha(){
    $testObj = new IModel("goodss");
    $arr = $testObj->query();
    $this->list = $arr;
    $this->redirect('sha');
}
public function miao(){
    $id = IReq::get("id");
    $testObj = new IModel("goodss");
    $arr = $testObj->query("goods_id=$id");
    $num = $arr[0]['goods_num'];
    if($num>0){                //支持购买
        //库存减少
        $num-=1;
        $data = array(
            'goods_num'=>$num
        );
        $testObj->setData($data);
        $a = $testObj->update("goods_id=$id");
    if($a){
        echo "<script>alert('购买成功');location.href='http://localhost/test/iwebshop4.6/index.php?controller=text&action=sha'</script>";
    }else{
        echo "<script>alert('购买失败，请稍后重试!');location.href='http://localhost/test/iwebshop4.6/index.php?controller=text&action=sha'</script>";
    }
    }else{
        echo "<script>alert('不好意思，库存不足!');location.href='http://localhost/test/iwebshop4.6/index.php?controller=text&action=sha'</script>";
    }
}