哪吒Java技能树--MyBaits学习笔记--关联和集合对应着多对一和一对多（“最易懂得MyBatis学习”）（下）

@Data
public class Student {
    private int id;
    private String name;
    private int tid;
}

@Data
public class Teacher {
    private int id;
    private String name;
    //一个老师拥有多个学生
    private List<Student> students;
}

public interface TeacherMapper {
    //获取所有老师
    //List<Teacher> getTeacher();
    //获取指定老师下的所有学生及老师的信息
    Teacher getTeacher(@Param("tid") int id);
    Teacher getTeacher2(@Param("tid") int id);
}

<select id="getTeacher" resultMap="TeacherStudent">
    select s.id sid, s.name sname,t.name tname,t.id tid from student s,teacher t where t.id = s.tid and t.id = #{tid};
</select>
<!--按结果嵌套查询-->
<resultMap id="TeacherStudent" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <!--复杂的属性，我们需要单独处理. 对象：association   集合：collection -->
    <!--javaType=""指定属性的类型！
    集合中的泛型信息，我们使用ofType获取
    -->
    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

<select id="getTeacher2" resultMap="TeacherStudent2">
    select * from teacher where id = #{tid}
</select>
<resultMap id="TeacherStudent2" type="Teacher">
    <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
</resultMap>
<select id="getStudentByTeacherId" resultType="Student">
    select * from student where tid = #{tid}
</select>