mybatis 一对多

 

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

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

<?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.rzk.mapper.TeacherMapper">
    <!--按结果嵌套查询 resultMap对应下面resultMap的id-->
    <select id="getTeacher" resultMap="TeacherStudent">
        select s.id sid, s.name sname,t.id tid,t.name tname
        from teacher t ,student s
        where s.tid = t.id AND t.id = #{tid}
    </select>
    <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>

@Test
public void getStudentByTeacher(){
  SqlSession sqlSessionFactory = MybatisUtils.getSqlSessionFactory();
  TeacherMapper mapper = sqlSessionFactory.getMapper(TeacherMapper.class);
  Teacher teacher2 = mapper.getTeacher2(1);
  System.out.println(teacher2);

  sqlSessionFactory.close();
}

    <!--Teacher(id=1, name=精致的猪猪女孩,
    students=[Student
            (id=1, name=小明, tid=1),
    Student(id=2, name=小红, tid=1),
    Student(id=3, name=小张, tid=1),
    Student(id=4, name=小李, tid=1),
    Student(id=5, name=小王, tid=1)])-->