多对一映射处理

标签：映射 dept 处理 查询 did emp select eid

查询员工信息以及员工所对应的部门信息

a>级联方式处理映射关系

<resultMap id="empDeptMap" type="Emp">
<id column="eid" property="eid"></id>
<result column="ename" property="ename"></result>
<result column="age" property="age"></result>
<result column="sex" property="sex"></result>
<result column="did" property="dept.did"></result>
<result column="dname" property="dept.dname"></result>
</resultMap>
<!--Emp getEmpAndDeptByEid(@Param("eid") int eid);-->
<select id="getEmpAndDeptByEid" resultMap="empDeptMap">
select emp.*,dept.* from t_emp emp left join t_dept dept on emp.did =
dept.did where emp.eid = #{eid}
</select>

b>使用association处理映射关系

<resultMap id="empDeptMap" type="Emp">
<id column="eid" property="eid"></id>
<result column="ename" property="ename"></result>
<result column="age" property="age"></result>
<result column="sex" property="sex"></result>
<association property="dept" javaType="Dept">
<id column="did" property="did"></id>
<result column="dname" property="dname"></result>
</association>
</resultMap>
<!--Emp getEmpAndDeptByEid(@Param("eid") int eid);-->
<select id="getEmpAndDeptByEid" resultMap="empDeptMap">
select emp.*,dept.* from t_emp emp left join t_dept dept on emp.did =
dept.did where emp.eid = #{eid}
</select>

c>分步查询

1）查询员工信息

/**
* 通过分步查询查询员工信息
* @param eid
* @return
*/
Emp getEmpByStep(@Param("eid") int eid);
<resultMap id="empDeptStepMap" type="Emp">
<id column="eid" property="eid"></id>
<result column="ename" property="ename"></result>
<result column="age" property="age"></result>
<result column="sex" property="sex"></result>
<!--
select：设置分步查询，查询某个属性的值的sql的标识（namespace.sqlId）
column：将sql以及查询结果中的某个字段设置为分步查询的条件
-->

<association property="dept"
select="com.atguigu.MyBatis.mapper.DeptMapper.getEmpDeptByStep" column="did">
</association>
</resultMap>

<!--Emp getEmpByStep(@Param("eid") int eid);-->

<select id="getEmpByStep" resultMap="empDeptStepMap">
select * from t_emp where eid = #{eid}

</select>

2）根据员工所对应的部门id查询部门信息

/**
* 分步查询的第二步：根据员工所对应的did查询部门信息
* @param did
* @return
*/
Dept getEmpDeptByStep(@Param("did") int did);
<!--Dept getEmpDeptByStep(@Param("did") int did);-->
<select id="getEmpDeptByStep" resultType="Dept">
select * from t_dept where did = #{did}
</select>

 

标签：映射,dept,处理,查询,did,emp,select,eid
From： https://www.cnblogs.com/ai377377/p/16801902.html