MyBatis 注解查询一对多（@Results @One）

//在userMapper里：
@Results({
    @Result(property = "id", column = "id"),
    @Result(property = "username", column = "username"),
    @Result(property = "orders", column = "uid", javaType = List.class,
        many = @Many(select = "OrderMapper.findOrderByUserId"))
})
@Select("select * from User")
public List<Order> findUserAndOrders();


//在orderMapper里：
@Select("select * from orders where user_id = #{userId}")
public User findOrderByUserId(Integer userId);