mybatis一对多 多对一查询

//多对一 方法一

<!--按结果嵌套-->

<select id="getStudentAndTeacher2" resultMap="StudentTeacher2">
        select s.id as sid,s.name as sname,t.name as tname,s.tid
        from student s,teacher t
        where s.tid = t.id
    </select>
    
    <resultMap id="StudentTeacher2" type="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="Teacher">
            <result property="id" column="tid"/>
            <result property="name" column="tname"/>
        </association>
    </resultMap>

//多对一 方法二 子查询
<resultMap id="StudentTeacher" type="Student">
        <!--复杂的属性需要单独处理
            association：对象
            collection：集合
        -->
        <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
    </resultMap>

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

一对多

<select id="getTeacherList" resultType="com.my.pojo.Teacher">
        select * from teacher
    </select>
    
    <!--按结果嵌套-->
    <select id="getTeacherAndStudents" resultMap="TeacherStudent">
        select s.id sid,s.name sname,t.id tid,t.name tname
        from student s,teacher t
        where s.tid = t.id and t.id = #{id}
    </select>

    <resultMap id="TeacherStudent" type="Teacher">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <!--javaType：指定属性的类型    ofType：指定集合中的泛型信息-->
        <collection property="studentList" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>


    <!--按查询嵌套-->
    <select id="getTeacherAndStudents2" resultMap="TeacherStudent2">
        select * from teacher where id = #{id}
    </select>

    <resultMap id="TeacherStudent2" type="Teacher">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
        <collection column="id" property="studentList" javaType="ArrayList" ofType="Student" select="getStudents"/>
    </resultMap>

    <select id="getStudents" resultType="Student">
        select * from student where tid = #{id}
    </select>