一、需求分析
- 需求：查询所有用户的信息以及每个用户所属的组的信息
- 分析：一个用户可以有多个组，一个组也可以由多个用户。
- 多对多，可以设置一张中间表，该表存放的是用户表和组表的对应关系。
二、创建数据库和实体对象
User.java
package com.shyroke.entity;import java.util.List;public class User { private int id; private String userName; private String passWord; //一个用户有多个组 private List groupList; //隐藏get和set方法 ｝
Group.java
package com.shyroke.entity;import java.util.List;public class Group { private int id; private String group_name; private String group_num;//一个组有多个用户 private List userList;}
三、创建UserMapper.java接口和UserMapper.xml配置文件
UserMapper.java
package com.shyroke.mapper;import java.util.List;import com.shyroke.entity.User;public interface UserMapper { public List selectUserAndGroup();} UserMapper.xml
四、添加mapper到总配置文件
mybatis-config.xml：
五、测试
package com.shyrolk.firstMybatis;import java.io.IOException;import java.io.InputStream;import java.util.List;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 com.shyroke.entity.User;import com.shyroke.mapper.UserMapper;/** * Hello world! * */public class App { public static void main(String[] args) throws IOException { String resource = "resource/mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession session = sessionFactory.openSession(); UserMapper userMapper= session.getMapper(UserMapper.class); List userList = userMapper.selectUserAndGroup(); for(User user:userList){ System.out.println(user.getId()); System.out.println(user.getPassWord()); System.out.println(user.getUserName()); System.out.println(user.getGroupList()); } }} 结果：
