Order Payment Pipeline: Coupon + Flash Sale + Coins + Group Buy Four-Layer Price Calculation
An in-depth analysis of the `OrderService.checkOut` method in a NestJS project, demonstrating how to chain four layers of price calculation (flash sale, coupon, coins, group buy) and five subsystems within a Prisma transaction, covering optimistic lock debit, atomic inventory deduction, and a complete refund flow.
Tarsier Labs