如何使每销售一件商品库存数量就减一呢

销售指的是拍下减还是付款[HEAVY MINUS SIGN]呢

数据库

支付成功调用Action控制器里的接口，完成数据库里的商品库存数量-1

可以参考我写的积分兑换，差不多

if($goods['id']==18){
$add=array();
$add['uid'] = $this->uid;
$add['type'] = 3;
$add['card'] = "积分换购100元红包";
$add['affect_money'] = 100;
$add['card_num'] = 1;
$add['expired_time'] = strtotime("+1 months");
$add['add_time'] = time();
$add['add_ip'] = get_client_ip();
for ($i=0; $i < $num; $i++){
$newid= M('user_card')->add($add);}
}
if($newid){
$goods_save=array();
$goods_save['id'] = $goods['id'];
$goods_save['has_exchange'] = array('exp','`has_exchange`+1');
$goods_save['stock'] = array('exp','`stock`-1');
M('credits_goods')->save($goods_save);
ajaxmsg("兑换成功");
//$this->display("common:_footer");
}
else ajaxmsg("兑换失败",0);