MyBatis（18）- Mybatis多表操作（3）- 多对多

1 多对多

用户和角色。步骤：

1. 建立2张表，用户表、角色表
   让用户表和角色表具有多对多的关系。需要使用中间表，中间表包含各自的主键
2. 建立2个实体类：用户实体类和角色实体类。
   各自包含对方的集合引用
3. 建立2个配置文件
4. 实现配置
   （1）查询用户时，同时得到用户包含的角色信息
   （2）查询角色时，同时得到角色赋予的用户信息

---

DROP TABLE IF EXISTS `role`;

CREATE TABLE `role` (
  `ID` int(11) NOT NULL COMMENT '编号',
  `ROLE_NAME` varchar(30) default NULL COMMENT '角色名称',
  `ROLE_DESC` varchar(60) default NULL COMMENT '角色描述',
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) values (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校');


DROP TABLE IF EXISTS `user_role`;

CREATE TABLE `user_role` (
  `UID` int(11) NOT NULL COMMENT '用户编号',
  `RID` int(11) NOT NULL COMMENT '角色编号',
  PRIMARY KEY  (`UID`,`RID`),
  KEY `FK_Reference_10` (`RID`),
  CONSTRAINT `FK_Reference_10` FOREIGN KEY (`RID`) REFERENCES `role` (`ID`),
  CONSTRAINT `FK_Reference_9` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

insert  into `user_role`(`UID`,`RID`) values (41,1),(45,1),(41,2);

2 查询角色，同时得到角色的用户信息

2.1 sql测试

---

2.2 实体类

2.3 DAO

• IRoleDao.xml

<?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.tzb.dao.IRoleDao">
    
    <resultMap id="roleMap" type="Role">
        <id property="roleId" column="rid"></id>
        <result property="roleName" column="role_name"></result>
        <result property="roleDesc" column="role_desc"></result>

        <collection property="users" ofType="User">
            <id property="id" column="id"></id>
            <result property="username" column="username"></result>
            <result property="sex" column="sex"></result>
            <result property="birthday" column="birthday"></result>
            <result property="address" column="address"></result>
        </collection>

    </resultMap>

    <select id="findAll" resultMap="roleMap">
        select u.*,r.id as rid,r.role_name,r.role_desc  from role r
 left outer join user_role ur on r.id = ur.rid
 left outer join user u on u.id = ur.uid
</select>

</mapper>

2.4 单元测试

public class RoleTest {

    private InputStream in;
    private SqlSession sqlSession;
    private IRoleDao roleDao;

    @Before
    public void init() throws IOException {
        // 1.读取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.创建 SqlSessionFactory 工厂
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        // 3.使用工厂生产 SqlSession 对象
        sqlSession = factory.openSession();
        // 4.使用 SqlSession 创建DAO接口的代理对象
        roleDao = sqlSession.getMapper(IRoleDao.class);
    }

    @After
    public void destory() throws IOException {
        // 提交事务
        sqlSession.commit();
        //6.释放资源
        sqlSession.close();
        in.close();
    }

    @Test
    public void testFindAll(){
        List<Role> roles = roleDao.findAll();
        for (Role role : roles) {
            System.out.println("----每一个角色------");
            System.out.println(role);
            System.out.println(role.getUsers());
            System.out.println("====================");
        }
    }

}

3 查询用户，同时得到角色

3.1 sql 测试

3.2 实体类

3.3 DAO

public interface IUserDao {
    List<User> findAll();

    User findById(Integer userId);

}

• IUserDao.xml

<?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.tzb.dao.IUserDao">


    <select id="findById" parameterType="int" resultType="com.tzb.domain.User">
    select * from user where id=#{userId}
    </select>

    <resultMap id="userMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
        <result property="address" column="address"></result>

        <collection property="roles" ofType="Role">
            <id property="roleId" column="rid"></id>
            <result property="roleName" column="role_name"></result>
            <result property="roleDesc" column="role_desc"></result>
        </collection>
    </resultMap>

    <select id="findAll" resultMap="userMap">
        select u.*,r.id as rid,r.role_name,r.role_desc  from user u
         left outer join user_role ur on u.id = ur.uid
         left outer join role r on r.id = ur.rid
    </select>

</mapper>

3.4 单元测试

    @Test
    public void testFindAll(){
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println("---- 每个用户信息 ----");
            System.out.println(user);
            System.out.println(user.getRoles());
            System.out.println("======================");
        }
    }