多对一的处理

一、按照查询嵌套处理

沿用上一篇博客“复杂查询环境搭建”项目

1.1、StudentsMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.massimo.dao.StudentsMapper">

        <select id="getStudents" resultMap="StudentTeacher">
            select * from students
        </select>

        <resultMap id="StudentTeacher" type="Students">
            <result property="id" column="id"/>
            <result property="name" column="name"/>
			<!--复杂的属性：需要单独处理  对象association  集合：collection-->
            <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
        </resultMap>

        <select id="getTeacher" resultType="Teacher">
            select * from teacher where id = #{id}
        </select>

</mapper>

1.2、测试类MyTest

@Test
    public void getStudents(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentsMapper mapper = sqlSession.getMapper(StudentsMapper.class);
        List<Students> studentsList = mapper.getStudents();
        for (Students students : studentsList){
            System.out.println(students);
        }

        sqlSession.close();
    }

1.3、效果

二、按照结果嵌套处理

2.1、StudentsMapper.xml

<select id="getStudents2" resultMap="StudentTeacher2">
            select s.id sid , s.name sname ,t.name tname
            from students s , teacher t
            where s.tid = t.id;
        </select>

        <resultMap id="StudentTeacher2" type="Students">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <association property="teacher" javaType="Teacher">
                <result property="name" column="tname"/>
            </association>
        </resultMap>

2.2、测试类MyTest

    @Test
    public void getStudents(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        StudentsMapper mapper = sqlSession.getMapper(StudentsMapper.class);
        List<Students> studentsList = mapper.getStudents2();
        for (Students students : studentsList){
            System.out.println(students);
        }

        sqlSession.close();
    }

2.3、效果