左连接查询数据 left join

同理的Right

<select id="pageQuery" resultType="com.sky.vo.DishVO">
        select d.* , c.name as categoryName from dish d left outer join category c on d.category_id = c.id
        <where>
            <if test="name != null">
                and d.name like concat('%',#{name},'%')
            </if>
            <if test="categoryId != null">
                and d.category_id = #{categoryId}
            </if>
            <if test="status != null">
                and d.status = #{status}
            </if>
        </where>
        order by d.create_time desc
    </select>

事务机制，要么同时成功，要么同时失败

    //新增菜品
    @Override
    @Transactional
    public void saveWithFlavor(DishDTO dishDTO) {

        // 新增表菜品
        Dish dish = new Dish();
        BeanUtils.copyProperties(dishDTO,dish);
        dish.setImage("目前没有阿里云服务器OOS，先这样了..");
        dishMapper.insert(dish);
        Long dishId = dish.getId();// 获取到生成的ID,然后赋值到 dish_flavor这个表里面

        //新增口味,批量循环添加口味
        List<DishFlavor> flavors = dishDTO.getFlavors();
        if(!flavors.isEmpty() && flavors != null){

            // 设置dish_flavor表的菜单ID值
            flavors.forEach((item)->{
                item.setDishId(dishId);
            });

            //向口味表插入n条数据
            dishFlavorMapper.insertBatch(flavors);
        }

    }