Day6老師跳過的，減少購物車商品數(shù)量的響應，為節(jié)省篇幅，我寫在controller里：

??@PostMapping("/sub")

??public R<String> sub(@RequestBody SetmealDish setmealDish){

????Long userId=BaseContext.getCurrentId();

????LambdaQueryWrapper<ShoppingCart> queryWrapper = new LambdaQueryWrapper<>();

????if (setmealDish.getSetmealId() != null) {

??????Long setmealId = setmealDish.getSetmealId();

??????queryWrapper.eq(ShoppingCart::getSetmealId, setmealId).eq(ShoppingCart::getUserId, userId);

????} else {

??????Long dishId = setmealDish.getDishId();

??????queryWrapper.eq(ShoppingCart::getDishId, dishId).eq(ShoppingCart::getUserId, userId);

????}

????ShoppingCart shoppingCart = shoppingCartService.getOne(queryWrapper);

????if (shoppingCart != null) {

??????if (shoppingCart.getNumber() == 1) {

????????shoppingCartService.removeById(shoppingCart);

??????} else {

????????shoppingCart.setNumber(shoppingCart.getNumber() - 1);

????????shoppingCartService.updateById(shoppingCart);

??????}

??????return R.success("成功");

????} else {

??????return R.error("購物車中不存在該商品");

????}

??}