多對多對映就是兩個實體之間是多對多的關係，例如老師和學生之間，可能是一個老師對應多個學生，同理一個學生可能對多個老師，那麼怎麼使用Mybatis程式怎麼寫出多對多關係？？？
1.先在entity包中新建兩個實體類，一個是學生類，另一個就是教師類，以學生類為主體，完成多表查詢操作：

student類

package com.baidu.lmj.entity;

public class TStudent {
    private int id;
    private String username;
    private int cid;

    private TTeachter tea;

    public
 
 int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getCid() {
        return cid;
    }

    public
 
 void setCid(int cid) {
        this.cid = cid;
    }

    public TTeachter getTea() {
        return tea;
    }

    public void setTea(TTeachter tea) {
        this.tea = tea;
    }
}

teachter類

package com.baidu.lmj.entity;

import java.util.List;

public class TTeachter {

    private int id;
    private
 
 String tname;
    private List<TStudent> list;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getTname() {
        return tname;
    }
    public void setTname(String tname) {
        this.tname = tname;
    }
    public List<TStudent> getList() {
        return list;
    }
    public void setList(List<TStudent> list) {
        this.list = list;
    }
}

2.在dao包中分別建一個TTeachter.java和TStudent.java，並且定義一些常用的方法，方法如下所示:
TTeachter.java

package com.baidu.lmj.dao;

import java.util.List;

import com.baidu.lmj.entity.TTeachter;

public interface TTeachterdao {
    public List<TTeachter> SelectAllTTeachter();

    public List<TTeachter> SelectAllTTeachter1();
}

TStudent.java

package com.baidu.lmj.dao;

import java.util.List;

public interface TStudent {
    public List<TStudent> SelectAllStudent();

    public List<TStudent> SelectAllStudent1();
}

3.在entity包中建立TStudent.xml配置檔案，進行資料庫查詢配置：

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.baidu.lmj.dao.TStudentDao">

    <resultMap type="com.baidu.lmj.entity.TStudent" id="map01">

        <id column="sid" property="id"/>
        <result column="username" property="username"/>

        <collection property="tea" ofType="com.baidu.lmj.entity.TTeachter">

            <id column="tid" property="id"/>

            <result column="tname" property="tname"/>


        </collection>

    </resultMap>

    <select id="SelectAllStudent" resultMap="map01">

        select a.id AS sid,username,c.id AS tid,c.tname from t_student a INNER JOIN t_s_t b ON a.id=b.sid INNER JOIN t_teacher c ON b.tid=c.id

    </select>





    <resultMap type="com.baidu.lmj.entity.TStudent" id="map02">


            <id column="id" property="id"/>

            <result column="username" property="username"/>

            <collection property="tea" column="id" ofType="com.baidu.lmj.entity.TTeachter" select="id001">


                <id column="id" property="id"/>

                <result column="tname" property="tname"/>

            </collection>


    </resultMap>

    <select id="SelectAllStudent1" resultMap="map02">

        select * FROM t_student

    </select>

    <select id="id001" parameterType="int" resultType="com.baidu.lmj.entity.TTeachter">
            select * FROM t_s_t a INNER JOIN t_teacher b ON a.tid=b.id WHERE a.sid=1
    </select>
</mapper>

4.在biz包中新建TStudentBiz.java類，進行業務層構建

package com.baidu.lmj.biz;

import java.io.IOException;
import java.util.List;

import org.apache.ibatis.session.SqlSession;

import com.baidu.lmj.dao.TStudentDao;
import com.baidu.lmj.entity.TStudent;
import com.baidu.lmj.util.SessionFactory;

public class TStudentBiz {
    TStudentDao dao;

    public List<TStudent> getAllTStudent(){

        List<TStudent> list=null;

        try {
            SqlSession session=SessionFactory.getSession();

            dao=session.getMapper(TStudentDao.class);

            list=dao.SelectAllStudent();

            SessionFactory.ClosedSession(session);


        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }





        return list;
    }


public List<TStudent> getAllTStudent1(){

        List<TStudent> list=null;

        try {
            SqlSession session=SessionFactory.getSession();

            dao=session.getMapper(TStudentDao.class);

            list=dao.SelectAllStudent1();

            SessionFactory.ClosedSession(session);


        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }





        return list;
    }
}

5.在Main.java類裡面進行測試並執行，測試程式碼如下所示：

package com.baidu.lmj.Main;

import java.util.List;

import com.baidu.lmj.biz.TStudentBiz;
import com.baidu.lmj.entity.TStudent;
import com.baidu.lmj.entity.TTeachter;

public class Main1 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
//      TStudentBiz biz=new TStudentBiz();
//      
//      List<TStudent> list=biz.getAllTStudent();
//      
//      for(TStudent stu:list)
//      {
//          System.out.println("查詢的學生是"+stu.getUsername());
//          System.out.println("他的教師是************************");
//          
//          for(TTeachter te:stu.getTea())
//          {
//              System.out.println(te.getTname());
//          }
//          System.out.println("****************結束********************");
//      }
        TStudentBiz biz=new TStudentBiz();

        List<TStudent> list=biz.getAllTStudent1();

        for(TStudent stu:list)
        {
            System.out.println("查詢的學生是"+stu.getUsername());
            System.out.println("他的教師是************************");

            for(TTeachter te:stu.getTea())
            {
                System.out.println(te.getTname());
            }
            System.out.println("****************結束********************");
        }
    }

}