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MyBatis 詳解（一對一，一對多，多對多）

 ywasdfghjkl 2019-04-25

1、什么是MyBatis?

　　MyBatis 本是apache的一個開源項目iBatis, 2010年這個項目由apache software foundation 遷移到了google code，并且改名為MyBatis 。2013年11月遷移到Github。

　　iBATIS一詞來源于“internet”和“abatis”的組合，是一個基于Java的持久層框架。iBATIS提供的持久層框架包括SQL Maps和Data Access Objects（DAO）。

　　MyBatis 是支持普通 SQL查詢，存儲過程和高級映射的優(yōu)秀持久層框架。MyBatis 消除了幾乎所有的JDBC代碼和參數(shù)的手工設(shè)置以及結(jié)果集的檢索。MyBatis 使用簡單的 XML或注解用于配置和原始映射，將接口和 Java 的POJOs（Plain Ordinary Java Objects，普通的 Java對象）映射成數(shù)據(jù)庫中的記錄。

PS:本文所有代碼下載鏈接：http://pan.baidu.com/s/1gf8CPQN 密碼：t2x9 

　　再給大家推薦一個比較好的mybatis學(xué)習(xí)網(wǎng)站：www.

2、MyBatis 入門實例基于xml配置

　　①、創(chuàng)建MySQL數(shù)據(jù)庫：mybatisDemo和表：person

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create database mybatisDemo;
use mybatisDemo;
create table person(pid int primary key AUTO_INCREMENT, pname varchar(50), page int);

　　

　　②、建立一個Java工程，并導(dǎo)入相應(yīng)的jar包

 　　

　　相應(yīng)的 jar 包下載鏈接：http://pan.baidu.com/s/1skZM09Z  密碼：nkt6

 　　③、在 MyBatisDemo 工程中添加數(shù)據(jù)庫配置文件 mybatis-configuration.xml

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<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE configuration PUBLIC '-////DTD Config 3.0//EN' 'http:///dtd/mybatis-3-config.dtd'>
<configuration>
<!-- 可以配置多個運行環(huán)境，但是每個 SqlSessionFactory 實例只能選擇一個運行環(huán)境  
  一、development:開發(fā)模式
   二、work：工作模式-->
 <environments default='development'>
 <!--id屬性必須和上面的default一樣  -->
    <environment id='development'>
    <!--事務(wù)管理器
        一、JDBC：這個配置直接簡單使用了 JDBC 的提交和回滾設(shè)置。它依賴于從數(shù)據(jù)源得到的連接來管理事務(wù)范圍
        二、MANAGED：這個配置幾乎沒做什么。它從來不提交或回滾一個連接。而它會讓容器來管理事務(wù)的整個生命周期
            比如 spring 或 JEE 應(yīng)用服務(wù)器的上下文，默認情況下，它會關(guān)閉連接。然而一些容器并不希望這樣，
            因此如果你需要從連接中停止它，就可以將 closeConnection 屬性設(shè)置為 false，比如：
            <transactionManager type='MANAGED'>
                <property name='closeConnection' value='false'/>
            </transactionManager>
      -->
      <transactionManager type='JDBC'/>
      <!--dataSource 元素使用標準的 JDBC 數(shù)據(jù)源接口來配置 JDBC 連接對象源  -->
      <dataSource type='POOLED'>
        <property name='driver' value='com.mysql.jdbc.Driver'/>
        <property name='url' value='jdbc:mysql://localhost:3306/mybatisdemo'/>
        <property name='username' value='root'/>
        <property name='password' value='root'/>
      </dataSource>
    </environment>
  </environments>
</configuration>

　　④、定義表所對應(yīng)的實體類

　　

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package com.ys.bean;
public class Person {
    private int pid;
    private String pname;
    private int page;
     
    public int getPid() {
        return pid;
    }
    public void setPid(int pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public int getPage() {
        return page;
    }
    public void setPage(int page) {
        this.page = page;
    }
    @Override
    public String toString() {
        return 'Person [pid=' + pid + ', pname=' + pname + ', page=' + page
                + ']';
    }
}

　　⑤、定義操作 person 表的sql映射文件personMapper.xml

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper
  PUBLIC '-////DTD Mapper 3.0//EN'
  'http:///dtd/mybatis-3-mapper.dtd'>
<mapper namespace='com.ys.bean.personMapper'>
  <!-- 根據(jù) pid 查詢 person 表中的數(shù)據(jù)
       id:唯一標識符，此文件中的id值不能重復(fù)
       resultType:返回值類型，一條數(shù)據(jù)庫記錄也就對應(yīng)實體類的一個對象
       parameterType:參數(shù)類型，也就是查詢條件的類型
   -->
  <select id='selectPersonById'
            resultType='com.ys.bean.Person' parameterType='int'>
    <!-- 這里和普通的sql 查詢語句差不多，對于只有一個查詢條件后面的 #{pid}表示占位符，里面不一定要寫pid,寫啥都可以，但是不要空著；如果有多個查詢條件，則要寫pojo類里面的屬性 -->
    select * from person where pid = #{pid}
  </select>
   
  <!-- 查詢person 表所有數(shù)據(jù) -->
  <select id='getAllPerson' resultType='com.ys.bean.Person'>
    select * from person
  </select>
   
  <!-- 根據(jù)id更新數(shù)據(jù) -->
  <update id='updatePersonById' parameterType='com.ys.bean.Person'>
    update person set pname=#{pname},page=#{page} where pid = #{pid}
  </update>
   
  <!-- 向 person 表插入一條數(shù)據(jù) -->
  <insert id='addPerson' parameterType='com.ys.bean.Person'>
    insert into person(pid,pname,page) values(#{pid},#{pname},#{page})
  </insert>
   
  <!-- 根據(jù) pid 刪除數(shù)據(jù) -->
  <delete id='deletePersonById' parameterType='Long'>
    delete from person where pid=#{pid}
  </delete>
   
</mapper>

　?、?strong>、向 mybatis-configuration.xml 配置文件中注冊 personMapper.xml 文件

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<mappers>
       <!-- 注冊personMapper.xml文件，
       personMapper.xml位于com.ys.bean這個包下，所以resource寫成com/ys/bean/personMapper.xml-->
       <mapper resource='com/ys/bean/personMapper.xml'/>
</mappers>

　　如下圖所示：

 　　⑦、創(chuàng)建測試類

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package com.ys.test;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.bean.Person;
public class MyBatisTest {
    SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加載 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream('mybatis-configuration.xml');
        //構(gòu)建sqlSession的工廠
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根據(jù) sqlSessionFactory 產(chǎn)生 session
        session = sqlSessionFactory.openSession();
    }
     
    //根據(jù) pid 查詢 person 表中的數(shù)據(jù)
    @Test
    public void testSelectById(){
        //這個字符串有 personMapper.xml 文件中 兩個部分構(gòu)成
        //<mapper namespace='com.ys.bean.personMapper'> 的 namespace 的值
        //<select id='selectPersonById' > id 值
        String statement = 'com.ys.bean.personMapper'+'.selectPersonById';
        Person p = session.selectOne(statement, 1);
        System.out.println(p);
        session.close();
    }
     
    //查詢person 表所有數(shù)據(jù)
    @Test
    public void testGetAllPerson(){
        String statement = 'com.ys.bean.personMapper.getAllPerson';
        List<Person> listPerson = session.selectList(statement);
        System.out.println(listPerson);
        session.close();
    }
     
    //根據(jù)id更新數(shù)據(jù)
    @Test
    public void updateById(){
        String statement = 'com.ys.bean.personMapper.updatePersonById';
        Person p = new Person();
        p.setPid(1);
        p.setPname('aaa');
        p.setPage(11);
        session.update(statement, p);
        session.commit();
        session.close();
    }
     
    //向 person 表插入一條數(shù)據(jù)
    @Test
    public void addPerson(){
        String statement = 'com.ys.bean.personMapper.addPerson';
        Person p = new Person();
        //由于我們設(shè)置了主鍵的自增長機制，故這里不需要手動設(shè)置 pid 的值
        //p.setPid(1);
        p.setPname('add');
        p.setPage(11);
        session.insert(statement, p);
        session.commit();
        session.close();
    }
     
    //根據(jù) pid 刪除person 表中的數(shù)據(jù)
    @Test
    public void deletePersonById(){
        String statement = 'com.ys.bean.personMapper.deletePersonById';
        session.delete(statement, 1);
        session.commit();
        session.close();
         
    }
     
}

3、MyBatis 入門實例注解配置

 　　①、上面的前面四步都是一樣的，但是第五步不一樣，我們不需要創(chuàng)建 personMapper.xml 文件，首先在 src 目錄下創(chuàng)建 personMapper.java 文件

　　

　　　內(nèi)容如下：

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package com.ys.annocation;
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import com.ys.bean.Person;
public interface PersonMapper {
     
    @Insert('insert into person(pid,pname,page) values(#{pid},#{pname},#{page})')
    public int add(Person person);
     
    @Select('select * from person where pid = #{pid}')
    public Person getPerson(int pid);
     
    @Update('update person set pname=#{pname},page=#{page} where pid = #{pid}')
    public int updatePerson(Person preson);
     
    @Delete('delete from person where pid=#{pid}')
    public int deletePerson(int pid);
}

　?、?、向 mybatis-configuration.xml 配置文件中注冊 personMapper.xml 文件

 　　③、編寫測試類

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@Test
public void testAnnocation(){
    PersonMapper mapper = session.getMapper(PersonMapper.class);
    Person p = new Person();
    p.setPid(7);
    p.setPname('abc');
    p.setPage(11);
    //調(diào)用增加方法
    mapper.add(p);
    //調(diào)用查詢方法
    Person p1 = mapper.getPerson(3);
    System.out.println(p1);
    //調(diào)用更新方法
    p.setPage(100);
    mapper.updatePerson(p);
    //調(diào)用刪除方法
    mapper.deletePerson(7);
    session.commit();
    session.close();
}

4、MyBatis 入門實例  一對一  基于xml配置

　　這里我們以老師和班級為例，假設(shè)一般班級只能擁有有一個老師，一個老師只能帶一個班級。

　　①、創(chuàng)建實體類

　　

　　Teacher.java

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package one.to.one;
public class Teacher {
    private int tid;
    private String tname;
    private Classes classes;
     
    public int getTid() {
        return tid;
    }
    public void setTid(int tid) {
        this.tid = tid;
    }
    public String getTname() {
        return tname;
    }
    public void setTname(String tname) {
        this.tname = tname;
    }
    public Classes getClasses() {
        return classes;
    }
    public void setClasses(Classes classes) {
        this.classes = classes;
    }
    @Override
    public String toString() {
        return 'Teacher [tid=' + tid + ', tname=' + tname + ', classes=' + classes + ']';
    }
     
     
}

　　Classes.java

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package one.to.one;
public class Classes {
    private int cid;
    private String cname;
    private Teacher teacher;
     
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Teacher getTeacher() {
        return teacher;
    }
    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
    @Override
    public String toString() {
        return 'Classes [cid=' + cid + ', cname=' + cname + ', teacher=' + teacher + ']';
    }
     
}

　　②、在數(shù)據(jù)庫中根據(jù)實體類創(chuàng)建相應(yīng)的數(shù)據(jù)表

　　③、定義操作 Classes 表的sql映射文件classesMapper.xml　

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper
  PUBLIC '-////DTD Mapper 3.0//EN'
  'http:///dtd/mybatis-3-mapper.dtd'>
<mapper namespace='one.to.one.classesMapper'>
    <!--
         方式一：嵌套結(jié)果：使用嵌套結(jié)果映射來處理重復(fù)的聯(lián)合結(jié)果的子集
                 封裝聯(lián)表查詢的數(shù)據(jù)(去除重復(fù)的數(shù)據(jù))
         select * from classes c, teacher t where c.tid=t.tid and c.tid=#{tid}
     -->
    <select id='getClasses' resultMap='getClassesMap' parameterType='int'>
        select * from classes c ,teacher t
            where c.tid=t.tid and c.tid=#{tid}
    </select>
    <resultMap type='one.to.one.Classes' id='getClassesMap'>
        <id column='cid' property='cid'/>
        <result column='cname' property='cname'/>
        <association property='teacher' javaType='one.to.one.Teacher'>
            <id column='tid' property='tid'></id>
            <result column='tname' property='tname'/>
        </association>
    </resultMap>
    <!--
         方式一：嵌套結(jié)果：使用嵌套結(jié)果映射來處理重復(fù)的聯(lián)合結(jié)果的子集
                 封裝聯(lián)表查詢的數(shù)據(jù)(去除重復(fù)的數(shù)據(jù))
         select * from teacher t,classes c where t.cid = c.cid and t.cid=#{cid}
     -->
    <select id='getTeacher' resultMap='getTeacherMap' parameterType='int'>
        select * from teacher t,classes c
            where t.cid = c.cid and t.cid=#{cid}
    </select>
    <resultMap type='one.to.one.Teacher' id='getTeacherMap'>
        <id column='tid' property='tid'/>
        <result column='tname' property='tname'/>
        <association property='classes' javaType='one.to.one.Classes'>
            <id column='cid' property='cid'/>
            <result column='cname' property='cname'/>
        </association>
    </resultMap>
     
     
    <!--
         方式二：嵌套查詢：通過執(zhí)行另外一個SQL映射語句來返回預(yù)期的復(fù)雜類型
         SELECT * FROM classes WHERE cid=1;
         SELECT * FROM teacher WHERE tid=1   //1 是上一個查詢得到的tid的值
         property:別名(屬性名)    column：列名 -->
          <!-- 把teacher的字段設(shè)置進去 -->
    <select id='getClasses2' resultMap='getClassesMap2'>
        select * from classes c where c.cid = #{cid}
    </select>
    <resultMap type='one.to.one.Classes' id='getClassesMap2'>
        <id column='cid' property='cid'/>
        <result column='cname' property='cname'/>
        <collection property='teacher' column='tid' select='getTeacherCollection'>
        </collection>
    </resultMap>
    <select id='getTeacherCollection' resultType='one.to.one.Teacher'>
        select tid tid,tname tname from teacher where tid=#{tid}
    </select>
   
</mapper>

　　說明：我們這里一對一的關(guān)聯(lián)操作，有兩種方式：

　　　　1、使用嵌套結(jié)果映射來處理重復(fù)的聯(lián)合結(jié)果的子集

　　　　2、通過執(zhí)行另外一個SQL映射語句來返回預(yù)期的復(fù)雜類型

　　　　相關(guān)屬性解釋：

　　　　

　?、?、向 mybatis-configuration.xml 配置文件中注冊 classesMapper.xml 文件

　　

　　⑤、編寫測試類

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package one.to.one;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.test.MyBatisTest;
public class OneToOneTest {
SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加載 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream('mybatis-configuration.xml');
        //構(gòu)建sqlSession的工廠
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根據(jù) sqlSessionFactory 產(chǎn)生 session
        session = sqlSessionFactory.openSession();
    }
     
    //一對一嵌套結(jié)果方式：根據(jù)教師id查詢班級信息
    @Test
    public void testGetClasses(){
        String statement = 'one.to.one.classesMapper.getClasses';
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
    }
     
    //一對一嵌套結(jié)果方式：根據(jù)班級id查詢教師信息
    @Test
    public void testGetTeacher(){
        String statement = 'one.to.one.classesMapper.getTeacher';
        Teacher t = session.selectOne(statement, 1);
        System.out.println(t);
    }
     
    //一對一嵌套查詢方式：根據(jù)教師id查詢班級信息
    @Test
    public void testGetClasses2(){
        String statement = 'one.to.one.classesMapper.getClasses2';
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
    }
     
     
}

4、MyBatis 入門實例  一對多，多對一  基于xml配置

　　這里我們以班級和學(xué)生為例，一個班級里面對應(yīng)多個學(xué)生，這是一對多；反過來，多個學(xué)生對應(yīng)一個班級，這是多對一

　　①、建立學(xué)生和班級的實體類

　　Student.java

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package one.to.many;
public class Student {
    private int sid;
    private String sname;
    private Classes classes;
    public int getSid() {
        return sid;
    }
    public void setSid(int sid) {
        this.sid = sid;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public Classes getClasses() {
        return classes;
    }
    public void setClasses(Classes classes) {
        this.classes = classes;
    }
    @Override
    public String toString() {
        return 'Student [sid=' + sid + ', sname=' + sname + ', classes=' + classes + ']';
    }
     
}

　　　　Classes.java

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package one.to.many;
import java.util.Set;
public class Classes {
    private int cid;
    private String cname;
    private Set<Student> students;
     
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
    @Override
    public String toString() {
        return 'Classes [cid=' + cid + ', cname=' + cname + ', students=' + students + ']';
    }
}

　　②、在數(shù)據(jù)庫中根據(jù)實體類創(chuàng)建相應(yīng)的數(shù)據(jù)表

　　③、多對一：定義操作 Classes 表的sql映射文件classesMapper.xml　

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper
  PUBLIC '-////DTD Mapper 3.0//EN'
  'http:///dtd/mybatis-3-mapper.dtd'>
<mapper namespace='one.to.many.classesMapper'>
    <select id='getClasses' resultMap='getClassesMap'>
        select * from classes c,student s where s.cid=c.cid and c.cid=#{cid}
    </select>
    <resultMap type='one.to.many.Classes' id='getClassesMap'>
        <id column='cid' property='cid'></id>
        <result column='cname' property='cname'/>
        <collection property='students' ofType='one.to.many.Student'>
            <id column='sid' property='sid'/>
            <result column='sname' property='sname'/>
        </collection>
    </resultMap>
     
</mapper>

　?、?、一對多：定義操作 Student 表的sql映射文件studentMapper.xml

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper
  PUBLIC '-////DTD Mapper 3.0//EN'
  'http:///dtd/mybatis-3-mapper.dtd'>
<mapper namespace='many.to.one.studentMapper'>
    <select id='getStudents' resultMap='getStudentMap'>
        select * from classes c,student s where s.cid=c.cid and s.sid=#{sid}
    </select>
    <resultMap type='one.to.many.Student' id='getStudentMap'>
        <id column='sid' property='sid'></id>
        <result column='sname' property='sname'/>
        <association property='classes' javaType='one.to.many.Classes'>
            <id column='cid' property='cid'/>
            <result column='cname' property='cname'/>
        </association>
    </resultMap>
     
</mapper>

　　⑤、向 mybatis-configuration.xml 配置文件中注冊 classesMapper.xml 、studentMapper.xml文件

　?、?、編寫測試類

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package one.to.many;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
import com.ys.test.MyBatisTest;
public class OneToManyTest {
SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加載 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream('mybatis-configuration.xml');
        //構(gòu)建sqlSession的工廠
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根據(jù) sqlSessionFactory 產(chǎn)生 session
        session = sqlSessionFactory.openSession();
    }
     
    //一對多嵌套結(jié)果方式：根據(jù)班級id查詢班級所有的學(xué)生信息
    @Test
    public void testGetClasses(){
        String statement = 'one.to.many.classesMapper.getClasses';
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
        System.out.println(c.getStudents().size());
    }
     
     
    //多對一嵌套結(jié)果方式：根據(jù)學(xué)生id查詢班級信息
    @Test
    public void testGetStudents(){
        String statement = 'many.to.one.studentMapper.getStudents';
        Student s = session.selectOne(statement, 1);
        System.out.println(s);
        System.out.println(s.getClasses());
    }
     
     
}

5、MyBatis 入門實例  多對多  基于xml配置

　　這里我們以 users 表和 groups 表為例，一個 users 可能加入多個 groups，而一個 groups 可能包含多個 users，故構(gòu)成 多對多 的關(guān)聯(lián)

　　①、在數(shù)據(jù)庫中建立相應(yīng)的表

　　users 表

　　

　　groups 表

　　

　　兩者之間的關(guān)聯(lián)表users_groups表

　　

　　②、建立對應(yīng)的實體類

　　Users.java

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package many.to.many;
import java.util.Set;
public class Users {
    private int uid;
    private String uname;
    private Set<Groups> groups;
    public int getUid() {
        return uid;
    }
    public void setUid(int uid) {
        this.uid = uid;
    }
    public String getUname() {
        return uname;
    }
    public void setUname(String uname) {
        this.uname = uname;
    }
    public Set<Groups> getGroups() {
        return groups;
    }
    public void setGroups(Set<Groups> groups) {
        this.groups = groups;
    }
    @Override
    public String toString() {
        return 'User [uid=' + uid + ', uname=' + uname + ', groups=' + groups + ']';
    }
     
}

　　　　Groups.java

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package many.to.many;
import java.util.Set;
public class Groups {
    private int gid;
    private String gname;
    private Set<Users> users;
    public int getGid() {
        return gid;
    }
    public void setGid(int gid) {
        this.gid = gid;
    }
    public String getGname() {
        return gname;
    }
    public void setGname(String gname) {
        this.gname = gname;
    }
    public Set<Users> getUsers() {
        return users;
    }
    public void setUsers(Set<Users> users) {
        this.users = users;
    }
    @Override
    public String toString() {
        return 'Group [gid=' + gid + ', gname=' + gname + ', users=' + users + ']';
    }
     
}

　　　　Users_Groups.java

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package many.to.many;
public class Users_Groups {
    private Users user;
    private Groups group;
    public Users getUser() {
        return user;
    }
    public void setUser(Users user) {
        this.user = user;
    }
    public Groups getGroup() {
        return group;
    }
    public void setGroup(Groups group) {
        this.group = group;
    }
}

　?、邸⒍?strong>對多：定義操作 sql映射文件userMapper.xml

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<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE mapper
  PUBLIC '-////DTD Mapper 3.0//EN'
  'http:///dtd/mybatis-3-mapper.dtd'>
<mapper namespace='many.to.many.userMapper'>
    <!-- 給一個用戶 id，查看該用戶下的所有用戶組信息 -->
    <select id='getUsers' resultMap='getGroupMap'>
        select g.gid,g.gname from users_groups ug,groups g
            where ug.group_id=g.gid and ug.user_id=#{uid}
    </select>
    <resultMap type='many.to.many.Groups' id='getGroupMap'>
        <id column='gid' property='gid'/>
        <result column='gname' property='gname'/>
        <collection property='users' ofType='many.to.many.Users'>
            <id column='uid' property='uid'/>
        <result column='uname' property='uname'/>
        </collection>
    </resultMap>
     
</mapper>

　?、荨⑾?nbsp;mybatis-configuration.xml 配置文件中注冊 userMapper.xml文件

　?、蕖⒕帉憸y試類

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//多對多：根據(jù)根據(jù)用戶 id 查詢所有的用戶組信息
    @Test
    public void testGetGroups(){
        String statement = 'many.to.many.userMapper.getUsers';
        List<Groups> listGroup = session.selectList(statement,1);
        for(Groups g : listGroup){
            System.out.println(g.toString());
        }
    }

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