1、建立数据库表如下：

DROP TABLE IF EXISTS t_demo_user;CREATE TABLE IF NOT EXISTS t_demo_user(    userid varchar(255),    username varchar(100),    password varchar(100),    PRIMARY KEY(userid))ENGINE=InnoDB  DEFAULT CHARSET=gbk;insert into t_demo_user(userid, username, password) values("1001","fredric","fredric2001");DROP TABLE IF EXISTS t_demo_role;CREATE TABLE IF NOT EXISTS t_demo_role(    roleid int(20) NOT NULL AUTO_INCREMENT,    rolename varchar(100),    userid varchar(255),    FOREIGN KEY(userid) references t_demo_user(userid),    PRIMARY KEY(roleid))ENGINE=InnoDB  DEFAULT CHARSET=gbk AUTO_INCREMENT=1 ;insert into t_demo_role(rolename, userid) values("role1","1001"),("role2","1001");

2、建立对应的模型和接口JAVA

public class Role {    private int roleid;    private String rolename;    private String userid;

public class User {        private String userid;    private String username;    private String password;    private List
     
       roles;
     

public interface IUserOperation {    List
     
       queryAfterJoin();}
     

3、配置对应的XML文件如下：

     
          
                
                 
                 
                 
                     
                      
                
             
            
                SELECT            u.userid,            u.username,            u.password,          r.roleid roleid,           r.rolename rolename        FROM            t_demo_user u          LEFT JOIN            t_demo_role r          ON            u.userid = r.userid          
     

4、使用测试如下：

IUserOperation userOperation = session.getMapper(IUserOperation.class);List
     
       users = userOperation.queryAfterJoin();                for(User u:users){           System.out.println(u.getUserid());           System.out.println(u.getUsername());           System.out.println(u.getPassword());           List
      
        roles = u.getRoles();           for(Role r:roles){               System.out.println(r.getRolename());               System.out.println(r.getRoleid());          }                }                 session.commit();