级联关系实现的方式

• 一对一

• 一对多

案例实操

一对一关系

实现方式 resultType/resultMap

接口方法

/**

• 一对一关联查询 resultType

• @param userId

• @return

*/

UserDto queryUserCardInfoForResultType(@Param("userId")int userId);

sql 查询

SELECT u.id, u.user_name AS userName, u.user_pwd AS userPwd, u.flag, u.cid, c.number FROM USER u LEFT JOIN card c ON u.cid = c.id WHERE u.id = #{userId}

resultType 实现

SELECT u.id, u.user_name AS userName, u.create_time, u.flag, u.cid AS cid, c.number FROM User u LEFT JOIN card c u ON u.cid =c.id WHERE u.id = #{id}

resultMap 实现

SELECT u.id,u.user_name,u.true_name,l.role_name FROM t_user u JOIN t_user_role r ON (u.id = r.user_id) JOIN t_role l on (r.role_id = l.id) WHERE u.id = #{id}

resultMap + association实现

resultMap 映射定义

查询

SELECT id, role_id FROM t_user_role WHERE id = #{id} SELECT id, role_name , role_remark FROM t_role WHERE id = #{role_id}

一对多关系

实现方式:resultMap 实现

resultType 有局限，无法去重，需手动处理。

ResultMap 定义

查询

select id, name , promotePrice FROM yg_goods WHERE id = #{id} SELECT id , goods_skuid , goods_img FROM yg_goods_imgage where goods_skuid = #{id}

扩展

sql

sql 元素用来定义一个可以复用的 SQL 语句段，供其它语句调用。比如：

userId, userName, password

select from user where userId = #{userId}