mybatis-一对多查询的模型 resultMap+collection

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户，一对多查询的需求：查询一个用户，与此同时查询出该用户具有的订单

对应的sql语句：select *,o.id oid from user u left join orders o on u.id=o.uid;

1）修改User实体

public class Order {

    private int id;
    private Date ordertime;
    private double total;

    //代表当前订单从属于哪一个客户
    private User user;
}

public class User {
    private int id;
    private String username;
    private String password;
    private Date birthday;
    //代表当前用户具备哪些订单
    private List orderList;
}

2)创建UserMapper接口

public interface UserMapper {
    List findAll();
}

3)配置UserMapper.xml

    
        
        
        
        
        
        
            
            
            
            
        
    

    
        SELECT *,o.id oid FROM USER u,orders o WHERE u.id=o.uid
    

4)测试结果

@Test
    public void test2() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List userList = mapper.findAll();
        for (User user : userList) {
            System.out.println(user);
        }

        sqlSession.close();
    }