Mybatis关联查询之多对多
多对多
一、entity实体类
public class Student {
private Integer stuid;
private String stuname;
private String stuaddress;
//植入一个Teacher集合，代表一名学员可以被多名教员教课
private List<Teacher> teachers;
public Integer getStuid() {
return stuid;
}
public void setStuid(Integer stuid) {
this.stuid = stuid;
}
public String getStuname() {
return stuname;
}
public void setStuname(String stuname) {
this.stuname = stuname;
}
public String getStuaddress() {
return stuaddress;
}
public void setStuaddress(String stuaddress) {
this.stuaddress = stuaddress;
}
public List<Teacher> getTeachers() {
return teachers;
}
public void setTeachers(List<Teacher> teachers) {
this.teachers = teachers;
}
}public class Teacher {
private Integer tid;
private String tname;
//植入学员集合，代表一名教员授课多名学生
private List<Student> students;
public Integer getTid() {
return tid;
}
public void setTid(Integer tid) {
this.tid = tid;
}
public String getTname() {
return tname;
}
public void setTname(String tname) {
this.tname = tname;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
}二、dao层
//多对多 查询所有学生信息 以及授课老师
public List<Student> getStudentInfo();
三、dao.xml小配置
<!--多对多-->
<resultMap id="studentAndTeacher" type="com.marketsys.entity.Student">
<id column="stuid" property="stuid"/>
<collection property="teachers" ofType="com.marketsys.entity.Teacher">
<id column="tid" property="tid"/>
</collection>
</resultMap>
<select id="getStudentInfo" resultMap="studentAndTeacher">
select * from student,teacher,stu_t where student.stuid=stu_t.stuid and teacher.tid=stu_t.tid
</select>
四、test测试类
SqlSession sqlSession= MybatisUtil.getSqlSession();
URoleTestDao mapper=sqlSession.getMapper(URoleTestDao.class);
//多对多
@Test
public void test3(){
List<Student> studentInfo = mapper.getStudentInfo();
for (Student stu:studentInfo) {
System.out.println("学生："+stu.getStuname());
for (Teacher teacher:stu.getTeachers()) {
System.out.print("\t教员："+teacher.getTname());
}
}
}