泽途新邦

 1 public List<OrderVO> getOrderList(Long userId) {
 2     // 查询用户所有订单
 3     List<Order> orders = orderMapper
 4         .selectByUserId(userId);
 5     List<OrderVO> result = new ArrayList<>();
 6     // ⚠️ N+1问题：循环中查询数据库
 7     for (Order order : orders) {
 8         Product product = productMapper
 9             .selectById(order.getPid());
10         User user = userMapper
11             .selectById(order.getUid());
12         OrderVO vo = new OrderVO();
13         vo.setOrder(order);
14         vo.setProduct(product);
15         vo.setUser(user);
16         result.add(vo);
17     }
18     return result;
19 }

 1 public List<OrderVO> getOrderList(Long userId) {
 2     List<Order> orders = orderMapper
 3         .selectByUserId(userId);
 4     if (CollectionUtils.isEmpty(orders)) {
 5         return Collections.emptyList();
 6     }
 7     // ✅ 批量查询，避免N+1问题
 8     Set<Long> pids = orders.stream()
 9         .map(Order::getPid)
10         .collect(Collectors.toSet());
11     Map<Long, Product> productMap = productMapper
12         .selectBatchIds(pids).stream()
13         .collect(Collectors.toMap(
14             Product::getId, p -> p));
15     // 内存中组装，0次额外查询
16     return orders.stream().map(o -> {
17         OrderVO vo = new OrderVO();
18         vo.setOrder(o);
19         vo.setProduct(productMap.get(o.getPid()));
20         return vo;
21     }).collect(Collectors.toList());
22 }