实训--经验总结5

Posted 2020-12-03 czy16

一对一，和一对多 。 mybatis写法

一对多：

DepEmpInfoDao.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.icss.dao.DepEmpInfoDao">
    <select id="getDepEmpByDepId" parameterType="int" resultMap="DepMap">
        select * from department d INNER JOIN employee e on e.d_id =e.d_id and
        e.d_id = #{id}
        </select>

    <resultMap type="Dep" id="DepMap">
        <id column="d_id" property="d_id" />
        <result column="dname" property="d_name" />
         <!--  装配一个集合  collection  申明集合中的元素类型ofType=-->
        <!-- collection 一对多  注意;ofType  一定要指明这个集合里的成员类型，不然报nullPorionException-->
        <collection property="employee" ofType="Emp">
            <id column="e_id" property="e_id" />
            <result column="empName" property="e_name" />
            <result column="job" property="e_job" />
            <result column="sal" property="sal" />
            <!-- <result column="d_id" property="d_id" /> -->
        </collection>
    </resultMap>
</mapper>