13、mybatis一对多resultMap中用collection指定集合的封装规则

一的一方College.java：

多的一方Student.java

College的sqlmapper文件配置

    <resultMap type="com.pxxy.bean.College" id="collegeMap">
        <id column="id" property="id"/>
        <result column="collegeName" property="collegeName"/>

        <!-- collection定义关联集合类型的属性的封装规则
                property：指定属性中集合的名称
                oftype：指定集合里面元素的类型；可以写别名-->
        <collection property="students" ofType="com.pxxy.bean.Student">
            <id column="s_id" property="id"/>
            <result column="name" property="name"/>
        </collection>
    </resultMap>

    <!-- 左连接查询 -->
    <select id="getColByIdPlus" resultMap="collegeMap">
        select c.id id,c.collegeName collegeName,s.id s_id,s.name name
        from college c
        left join student s
        on c.id = s.c_id
        where c.id=#{id}
    </select>

College的mapper接口方法

测试方法

    //测试根据id查询学校以及学校的学生
    @Test
    public void testGetColByIdPlus() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        CollegeMapper collegeMapper = sqlSession.getMapper(CollegeMapper.class);
        College college =  collegeMapper.getColByIdPlus(1);
        System.out.println(college);
        for(Student stu:college.getStudents()) {
            System.out.println(stu);
        }
        sqlSession.close();
    }

结果：

原文地址：https://www.cnblogs.com/lyh233/p/12350077.html