int s = dao.getStock(id);
if (s > 0) {
dao.decrStock(id);
order.create();
}
✅ 正确:原子扣减
// DB条件更新int n = dao.decrIfPositive(id);
// UPDATE SET stock=stock-1// WHERE id=? AND stock>0if (n==0) throw"售罄";
// 或 Redis 原子long left = redis.decr(key);
if (left<0){redis.incr(key);throw"售罄";}