MyBatis高级映射（一对多查询）

1、需求

查询所有订单及订单下的明细信息，订单与订单明细为一对多关系

2、数据库结构

user用户表



orders订单表



orders订单表外键



orderdetail订单详情表



orderdetail订单详情表外键



3、SQL语句



4、开始编码

4.1、定义POJO

User

package org.mybatis.demo.po;

import java.util.Date;

public class User {

//属性名和数据库表的字段对应
private int id;
private String username;// 用户姓名
private String sex;// 性别
private Date birthday;// 生日
private String address;// 地址

public int getId() {
return id;
}
public void setId(int 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 + "]";
}

}

Orders

package org.mybatis.demo.po;

import java.util.Date;
import java.util.List;

public class Orders {

private Integer id;
private Integer userId;
private String number;
private Date createtime;
private String note;
//用户信息
private User user;
//订单明细
private List<Orderdetail> orderdetails;

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();
}

public User getUser() {
return user;
}

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

public List<Orderdetail> getOrderdetails() {
return orderdetails;
}

public void setOrderdetails(List<Orderdetail> orderdetails) {
this.orderdetails = orderdetails;
}

}

OrdersDetail

package org.mybatis.demo.po;

public class Orderdetail {
private Integer id;

private Integer ordersId;

private Integer itemsId;

private Integer itemsNum;

public Integer getId() {
return id;
}

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

public Integer getOrdersId() {
return ordersId;
}

public void setOrdersId(Integer ordersId) {
this.ordersId = ordersId;
}

public Integer getItemsId() {
return itemsId;
}

public void setItemsId(Integer itemsId) {
this.itemsId = itemsId;
}

public Integer getItemsNum() {
return itemsNum;
}

public void setItemsNum(Integer itemsNum) {
this.itemsNum = itemsNum;
}

@Override
public String toString() {
return "Orderdetail [id=" + id + ", ordersId=" + ordersId
+ ", itemsId=" + itemsId + ", itemsNum=" + itemsNum + "]";
}

}

4.2、Mapper.xml

<?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="org.mybatis.demo.mapper.OrdersMapper">

<!-- 查询所有订单信息及订单下的订单明细信息，使用resultmap -->
<select id="findOrdersAndOrderDetailResultMap"
resultMap="OrdersAndOrderDetailResultMap">
SELECT
orders.*,
USER.username,
USER.sex,
USER.address,
orderdetail.id orderdetail_id,
orderdetail.items_id,
orderdetail.items_num,
orderdetail.orders_id
FROM
orders,
USER,
orderdetail
WHERE orders.user_id = user.id AND orderdetail.orders_id=orders.id
</select>

<!-- 订单及订单明细的resultMap
使用extends继承，不用在中配置订单信息和用户信息的映射
-->
<resultMap type="org.mybatis.demo.po.Orders" id="OrdersAndOrderDetailResultMap"
extends="OrdersUserResultMap">
<!-- 订单信息 -->
<!-- 用户信息 -->
<!-- 使用extends继承，不用在中配置订单信息和用户信息的映射 -->

<!-- 订单明细信息
一个订单关联查询出了多条明细，要使用collection进行映射
collection：对关联查询到多条记录映射到集合对象中
property：将关联查询到多条记录映射到cn.itcast.mybatis.po.Orders哪个属性
ofType：指定映射到list集合属性中pojo的类型
-->
<collection property="orderdetails" ofType="org.mybatis.demo.po.Orderdetail">
<!-- id：订单明细唯 一标识
property:要将订单明细的唯 一标识 映射到org.mybatis.demo.po.Orderdetail的哪个属性
-->
<id column="orderdetail_id" property="id"/>
<result column="items_id" property="itemsId"/>
<result column="items_num" property="itemsNum"/>
<result column="orders_id" property="ordersId"/>
</collection>
</resultMap>

<!-- 订单查询关联用户的resultMap
将整个查询的结果映射到cn.itcast.mybatis.po.Orders中
-->
<resultMap type="org.mybatis.demo.po.Orders" id="OrdersUserResultMap">
<!-- 配置映射的订单信息 -->
<!-- id：指定查询列中的唯 一标识，订单信息的中的唯 一标识，如果有多个列组成唯一标识，配置多个id
column：订单信息的唯 一标识 列
property：订单信息的唯 一标识 列所映射到Orders中哪个属性
-->
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="number" property="number"/>
<result column="createtime" property="createtime"/>
<result column="note" property="note"/>

<!-- 配置映射的关联的用户信息 -->
<!-- association：用于映射关联查询单个对象的信息
property：要将关联查询的用户信息映射到Orders中哪个属性
-->
<association property="user"  javaType="org.mybatis.demo.po.User">
<!-- id：关联查询用户的唯 一标识
column：指定唯 一标识用户信息的列
javaType：映射到user的哪个属性
-->
<id column="user_id" property="id"/>
<result column="username" property="username"/>
<result column="sex" property="sex"/>
<result column="address" property="address"/>
</association>
</resultMap>

</mapper>

4.3、Mapper接口

package org.mybatis.demo.mapper;

import java.util.List;

import org.mybatis.demo.po.Orders;

public interface OrdersMapper {

public List<Orders> findOrdersAndOrderDetailResultMap();
}

4.4、单元测试

package org.mybatis.demo.test;

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 org.junit.Before;
import org.junit.Test;
import org.mybatis.demo.mapper.OrdersMapper;
import org.mybatis.demo.po.Orderdetail;
import org.mybatis.demo.po.Orders;

public class TestMyBatis {

private SqlSessionFactory sessionFactory;

@Before
public void createSqlSessionFactory() throws IOException {
//引入配置文件
String resource = "SqlMapConfig.xml";
InputStream ins = Resources.getResourceAsStream(resource);

//创建SqlSession对象
sessionFactory = new SqlSessionFactoryBuilder().build(ins);
}

@Test
public void test1() {
SqlSession session = null;
try {
session = sessionFactory.openSession();
OrdersMapper mapper = session.getMapper(OrdersMapper.class);
List<Orders> list = mapper.findOrdersAndOrderDetailResultMap();
for(Orders order : list){
System.out.println(order.getUser().getUsername());
System.out.println("########");
for(Orderdetail detial:order.getOrderdetails()){
System.out.println("orderID:" + detial.getId());
}
}
} finally {
if(session != null){
session.close();
}
}
}

}

4.5、源代码

MyBatis高级映射（一对多查询）