db.go

func BuyHandler(buyRequest BuyRequest) {
    for i:=0; i<MaxRetry; i++ {
        needRetry := func() (retry bool) {
            defer func() {
                if err := recover(); err != nil {
                    if _, isTxConflic := err.(ErrTransactionConflic); isTxConflic {
                        retry = true;
                    }
                }
            }()
            BuyLogic();
            return retry
        }()
        if !needRetry {
            return;
        } 
    }
}

func BuyLogic(accountKey, goodsID int64) {
    tx = db.Begin()

    account, err := tx.LoadEntity(EntityType_Account, accountKey)
    if err != nil {
        panic(err)
    }

    goods, err := tx.LoadEntity(EntityType_Goods, goodsID)
    if err != nil {
        panic(err)
    }

    goodsDetail := goods.Detail.Lookup()
    if goodsDetail.Stocks <= 0 {
        tx.Rollback();
        return status.StockNotEnough("blablabla");
    }

    credit := account.Credit.Lookup()
    if goodsDetail.Price > credit.Balance {
        tx.Rollback()
        return status.BalanceNotEnough("blablabla")
    }

    goodsDetail.Stocks--
    credit.Balance -= goodsDetail.Price
    goods.Detail.Update(goodsDetail)
    account.Credit.Update(credit)

    tx.Commit()    
}