Two ways mybatis many queries

user and order objects

package com.itheima.mybatis.pojo;

import java.io.Serializable;
import java.util.Date;

public class Orders  implements Serializable{
    @Override
	public String toString() {
		return "Orders [id=" + id + ", userId=" + userId + ", number=" + number + ", createtime=" + createtime
				+ ", note=" + note + "]";
	}

	
	private static final long serialVersionUID = 1L;

	private Integer id;

    private Integer userId;

    private String number;

    private Date createtime;

    private String note;
    
    //附加对象  用户对象
    private User user;
    
  public User getUser() {
		return user;
	}

	public void setUser(User user) {
		this.user = user;
	}

	public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number == null ? null : number.trim();
    }

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note == null ? null : note.trim();
    }

    
    
}


package com.itheima.mybatis.pojo;

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class User implements Serializable {

	private static final long serialVersionUID = 1L;
	private Integer id;
	private String username;// 用户姓名
	private String sex;// 性别
	private Date birthday;// 生日
	private String address;// 地址
	
	//附加对象List
	private List<Orders> ordersList;
	public List<Orders> getOrdersList() {
		return ordersList;
	}
	public void setOrdersList(List<Orders> ordersList) {
		this.ordersList = ordersList;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public Date getBirthday() {
		return birthday;
	}
	public void setBirthday(Date birthday) {
		this.birthday = birthday;
	}
	public String getAddress() {
		return address;
	}
	public void setAddress(String address) {
		this.address = address;
	}
	@Override
	public String toString() {
		return "User [id=" + id + ", username=" + username + ", sex=" + sex + ", birthday=" + birthday + ", address="
				+ address + ", ordersList=" + ordersList + "]";
	}
	
	

	
	

}

mapper file

package com.itheima.mybatis.mapper;

import java.util.List;

import com.itheima.mybatis.pojo.User;

public interface TestMapper {

	public List<User> getUser();

	public List<User> getUser2();
}

mapper.xml file

<?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.itheima.mybatis.mapper.TestMapper">

	<resultMap type="User" id="user">
		<id property="id" column="userid" />
		<result property="username" column="username" />
		<result property="sex" column="sex" />
		<result property="birthday" column="birthday" />
		<result property="address" column="address" />
		<collection property="ordersList" ofType="Orders">
			<id property="id" column="orderid" />
			<result property="number" column="number" />
			<result property="createtime" column="createtime" />
			<result property="note" column="note" />
		</collection>
	</resultMap>
	
	<resultMap type="User" id="user2">
		<id property="id" column="userid" />
		<result property="username" column="username" />
		<result property="sex" column="sex" />
		<result property="birthday" column="birthday" />
		<result property="address" column="address" />

		<collection property="ordersList" ofType="Orders" select="getOrders"
			column="userid">
		</collection>
	</resultMap>
	<resultMap type="Orders" id="orders">
		<id property="id" column="orderid" />
		<result property="number" column="number" />
		<result property="createtime" column="createtime" />
		<result property="note" column="note" />
	</resultMap>
	<!-- 一对多查询的第一种方式 -->
	<select id="getUser" resultMap="user">
		SELECT
		u.id AS userid,
		u.username,
		u.birthday,
		u.sex,
		u.address,
		o.id AS orderid,
		o.number,
		o.CREATEtime,
		o.note
		FROM
		USER u
		LEFT JOIN orders o ON o.user_id = u.id
	</select>
	<!-- 一对多查询的 第二种方式 -->
	<select id="getUser2" resultMap="user2">
		SELECT
		u.id AS userid,
		u.username,
		u.birthday,
		u.sex,
		u.address,
		o.id AS orderid,
		o.number,
		o.CREATEtime,
		o.note
		FROM
		USER u
		LEFT JOIN orders o ON o.user_id = u.id
	</select>
	
	<select id="getOrders" parameterType="Integer" resultMap="orders">
		select
		o.id AS orderid,
		o.number,
		o.CREATEtime,
		o.note
		FROM orders o
		where
		o.user_id=#{id}
	</select>
</mapper>

@Test
	public void testMapper() throws Exception {
		//加载核心配置文件
		String resource = "sqlMapConfig.xml";
		InputStream in = Resources.getResourceAsStream(resource);
		//创建SqlSessionFactory
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
		//创建SqlSession
		SqlSession sqlSession = sqlSessionFactory.openSession();
		
		//SqlSEssion帮我生成一个实现类  （给接口）
		 TestMapper mapper = sqlSession.getMapper(TestMapper.class);
		 
		List<User> users = mapper.getUser2();
		for (User user : users) {
			System.out.println(user);
		}
		
	}