MyBatis（18）- Mybatis多表操作（3）- 多對多

1 多對多

用戶和角色。步驟：

1. 建立2張表，用戶表、角色表
   讓用戶表和角色表具有多對多的關係。需要使用中間表，中間表包含各自的主鍵
2. 建立2個實體類：用戶實體類和角色實體類。
   各自包含對方的集合引用
3. 建立2個配置文件
4. 實現配置
   （1）查詢用戶時，同時得到用戶包含的角色信息
   （2）查詢角色時，同時得到角色賦予的用戶信息

---

DROP TABLE IF EXISTS `role`;

CREATE TABLE `role` (
  `ID` int(11) NOT NULL COMMENT '編號',
  `ROLE_NAME` varchar(30) default NULL COMMENT '角色名稱',
  `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,'院長','管理整個學院'),(2,'總裁','管理整個公司'),(3,'校長','管理整個學校');


DROP TABLE IF EXISTS `user_role`;

CREATE TABLE `user_role` (
  `UID` int(11) NOT NULL COMMENT '用戶編號',
  `RID` int(11) NOT NULL COMMENT '角色編號',
  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 查詢角色，同時得到角色的用戶信息

2.1 sql測試

---

2.2 實體類

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 單元測試

public class RoleTest {

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

    @Before
    public void init() throws IOException {
        // 1.讀取配置文件
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.創建 SqlSessionFactory 工廠
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        // 3.使用工廠生產 SqlSession 對象
        sqlSession = factory.openSession();
        // 4.使用 SqlSession 創建DAO接口的代理對象
        roleDao = sqlSession.getMapper(IRoleDao.class);
    }

    @After
    public void destory() throws IOException {
        // 提交事務
        sqlSession.commit();
        //6.釋放資源
        sqlSession.close();
        in.close();
    }

    @Test
    public void testFindAll(){
        List<Role> roles = roleDao.findAll();
        for (Role role : roles) {
            System.out.println("----每一個角色------");
            System.out.println(role);
            System.out.println(role.getUsers());
            System.out.println("====================");
        }
    }

}

3 查詢用戶，同時得到角色

3.1 sql 測試

3.2 實體類

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 單元測試

    @Test
    public void testFindAll(){
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println("---- 每個用戶信息 ----");
            System.out.println(user);
            System.out.println(user.getRoles());
            System.out.println("======================");
        }
    }