本文共 5888 字，大约阅读时间需要 19 分钟。

我们知道，用户与角色之间存在多对多的关系：

关键配置1：

       
            
             
             
             
                 
                  
                  
              
         
        
            select u.*, r.id as rid, role, info from user u left outer join user_role ur on u.id = ur.uid         left outer join role r on ur.rid = r.id    
   

关键配置2：

       
        
        
        
            
             
             
         
    
       select r.*, u.id as uid, name, age from role r left outer join user_role ur on r.id = ur.rid      left outer join user u on ur.uid = u.id

最后附上源码：

项目结构：

pom.xml：

   
       
    
     4.0.0
        
    
     org.example
        
    
     P076_MyBatis_M2N
        
    
     1.0-SNAPSHOT
        
            
                 
      
       mysql
                  
      
       mysql-connector-java
                  
      
       8.0.16
              
             
                 
      
       org.mybatis
                  
      
       mybatis
                  
      
       3.4.5
              
             
                 
      
       junit
                  
      
       junit
                  
      
       4.12
                  
      
       test
              
         
    
   

数据库的相关信息：

MySQL：8.0.16    port：3306    database：multi_table

user表：

role表：

user_role表：

User类：

package cn.liuxingchang.domain;import java.io.Serializable;import java.util.List;public class User implements Serializable {    private Integer id;    private String name;    private Integer age;    private List
   
     roles;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    public List
    
      getRoles() {        return roles;    }    public void setRoles(List
     
       roles) {        this.roles = roles;    }    @Override    public String toString() {        return "User{" +                "id=" + id +                ", name='" + name + '\'' +                ", age=" + age +                ", roles=" + roles +                '}';    }}
     
    
   

Role类：

package cn.liuxingchang.domain;import java.io.Serializable;import java.util.List;public class Role implements Serializable {    private Integer id;    private String role;    private String info;    private List
   
     users;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getRole() {        return role;    }    public void setRole(String role) {        this.role = role;    }    public String getInfo() {        return info;    }    public void setInfo(String info) {        this.info = info;    }    public List
    
      getUsers() {        return users;    }    public void setUsers(List
     
       users) {        this.users = users;    }    @Override    public String toString() {        return "Role{" +                "id=" + id +                ", role='" + role + '\'' +                ", info='" + info + '\'' +                ", users=" + users +                '}';    }}
     
    
   

UserDao接口：

package cn.liuxingchang.dao;import cn.liuxingchang.domain.User;import java.util.List;public interface UserDao {    List
   
     findAll();}
   

RoleDao接口：

package cn.liuxingchang.dao;import cn.liuxingchang.domain.Role;import java.util.List;public interface RoleDao {    List
   
     findAll();}
   

UserMapper.xml：

   
       
            
             
             
             
                 
                  
                  
              
         
        
            select u.*, r.id as rid, role, info from user u left outer join user_role ur on u.id = ur.uid         left outer join role r on ur.rid = r.id    
   

RoleMapper.xml:

   
       
            
             
             
             
                 
                  
                  
              
         
        
            select r.*, u.id as uid, name, age from role r left outer join user_role ur on r.id = ur.rid          left outer join user u on ur.uid = u.id    
   

mybatis.xml:

Test.java:

import cn.liuxingchang.dao.RoleDao;import cn.liuxingchang.dao.UserDao;import cn.liuxingchang.domain.Role;import cn.liuxingchang.domain.User;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import org.junit.After;import org.junit.Before;import java.io.InputStream;import java.util.List;public class Test {    private InputStream in;    private SqlSessionFactory factory;    private SqlSession sqlSession;    private UserDao userDao;    private RoleDao roleDao;    @Before    public void before() throws Exception {        in = Resources.getResourceAsStream("mybatis.xml");        factory = new SqlSessionFactoryBuilder().build(in);        sqlSession = factory.openSession();        userDao = sqlSession.getMapper(UserDao.class);        roleDao = sqlSession.getMapper(RoleDao.class);    }    @After    public void after() throws Exception {        sqlSession.commit();        sqlSession.close();        in.close();    }    @org.junit.Test    public void findAllUsersTest() {        List
   
     users = userDao.findAll();        for (User user : users) {            System.out.println(user);        }    }    @org.junit.Test    public void findAllRolesTest() {        List
    
      roles = roleDao.findAll();        for(Role role: roles) {            System.out.println(role);        }    }}
    
   

转载地址：https://liuxingchang.blog.csdn.net/article/details/109102263 如侵犯您的版权，请留言回复原文章的地址，我们会给您删除此文章，给您带来不便请您谅解！