級(jí)聯(lián)關(guān)系實(shí)現(xiàn)的方式
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*? 一對(duì)一
*? 一對(duì)多
案例實(shí)操
----
### 一對(duì)一關(guān)系
實(shí)現(xiàn)方式 resultType/resultMap
**接口方法**
/**
?
* 一對(duì)一關(guān)聯(lián)查詢 resultType
?
* @param userId
?
* @return
?
*/
?
UserDto queryUserCardInfoForResultType(@Param("userId")int userId);
**sql 查詢**
<select id="queryUserCardInfoForResultType" resultType="userDto">
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}
</select>
#### resultType **實(shí)現(xiàn)**
<select id="queryUserByIdResultType" parameterType="int" resultType="com.xxx.dto.UserDto">
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}
</select>
#### resultMap 實(shí)現(xiàn)
<!--自定義映射關(guān)系實(shí)現(xiàn)關(guān)聯(lián)? -->
<resultMap id="baseUser" type="com.xxx.mybatis.pojo.User">
<id column="id"? property="id" /> <!-- 主鍵 -->
<!-- 普通例 -->
<result column="user_name" property="userName" />
<result column="true_name" property="trueName" />
<result column="role_name" property="roleName"/>
</resultMap>
<select id="queryUserInfoByIdV2"? parameterType="int" resultMap="baseUser" >
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}
</select>
#### resultMap + association實(shí)現(xiàn)
**resultMap** **映射定義**
<resultMap id="baseUserRole" type="userRole">
<id? column="id"? property="id"></id>
<result column="role_id"? property="roleId"></result>
<association property="role"? column="role_id" select="queryRoleById"/>
</resultMap>
?
<resultMap id="baseRole" type="role">
<id column="id" property="id"></id>
<result column="role_name" property="roleName"/>
<result column="role_remark" property="roleRemark"/>
</resultMap>
**查詢**
<select id="queryUserRoleInfoById" parameterType="int" resultMap="baseUserRole">
SELECT? id, role_id? FROM? t_user_role WHERE? id = #{id}
</select>
?
<select id="queryRoleById" parameterType="int"? resultMap="baseRole">
SELECT? id, role_name , role_remark? FROM t_role WHERE? id = #{role_id}
</select>
### 一對(duì)多關(guān)系
實(shí)現(xiàn)方式:resultMap 實(shí)現(xiàn)
resultType 有局限，無(wú)法去重，需手動(dòng)處理。
**ResultMap 定義**
<resultMap id="baseGoods" type="goods">
<id column="id" property="id"/>
<result column="name" property="goodsName"/>
<result column="promotePrice" property="price"/>
<collection property="ixxxs" column="id" select="queryGoodsIxxxsById"/>
</resultMap>
?
<resultMap id="baseGoodsImnage" type="GoodsIxxxs">
<id column="id" property="id"></id>
<result? column="goods_skuid" property="goodsSkuid" ></result>
<result? column="goods_img" property="ixxxUrl" ></result>
</resultMap>
查詢
<select id="queryGoodsById"? parameterType="int" resultMap="baseGoods" useCache="true">
select? id, name , promotePrice FROM yg_goods WHERE id = #{id}
</select>
?
<select id="queryGoodsIxxxsById" parameterType="int" resultMap="baseGoodsImnage" useCache="true">
SELECT id , goods_skuid , goods_img? FROM yg_goods_imgage where goods_skuid = #{id}
</select>
擴(kuò)展
--
### sql
sql 元素用來(lái)定義一個(gè)**可以復(fù)用的 SQL 語(yǔ)句段**，供其它語(yǔ)句調(diào)用。比如：
<sql id="User_columns">userId, userName, password</sql>
<!--用include 引用-->
<select id="findUserById" resultMap="RM_User" >
select <include refid="User_columns"/>
from user where userId = #{userId}
</select>
###
