乐观锁加事务扣余额，如何保证只扣一次且一次成功？

$user = $this->getuser(); //从数据库获取购买商品的用户信息$oldmoney = $user['balance']; //得到用户旧余额$orderoffer = $this->getordermoney($orderid); //获取次订单价格if($oldmoney < $orderoffer['price']) $this->error('账户余额不足');//乐观锁方案$newmoney = $oldmoney - $orderoffer['price']; //计算出新余额$newuser = smsuser::where(['id' => $user['id'],'balance' => $oldmoney])->find();if(!$newuser) $this->error('用户不存在');//开启数据库事务db::transaction(function () use($newuser,$orderid,$newmoney){    $newuser->balance = $newmoney;    $result = $newuser->save();    if(!$result) $this->error('保存余额失败');     //创建订单 code     //扣除库存 code     //创建用户余额变动记录 code        db::commit(); //提交事务         })

$user = $this->getUser(); //从数据库获取购买商品的用户信息$oldMoney = $user['balance']; //得到用户旧余额$orderOffer = $this->getOrderMoney($orderId); //获取次订单价格if($oldMoney < $orderOffer['price']) $this->error('账户余额不足');//乐观锁方案$newMoney = $oldMoney - $orderOffer['price']; //计算出新余额//开启数据库事务DB::transaction(function() use($user, $newMoney) {    $result = SmsUser::where(['id' => $user['id'], 'balance' => $oldMoney])        ->update(['balance' => $newMoney]);    if (!$result) throw new Exception('保存余额失败');        //创建订单 code    //扣除库存 code    //创建用户余额变动记录 code        DB::commit(); //提交事务});