MyBatis中的N+1问题，使用ResultSet来解决，需要存储过程【非常详细】

参考
https://mybatis.org/mybatis-3/zh/sqlmap-xml.html
https://mybatis.net.cn/sqlmap-xml.html#Result_Maps

基础表sql

订单表

CREATE TABLE `test_order` (`order_id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '订单id',`order_name` varchar(255) NOT NULL DEFAULT '' COMMENT '订单名字',PRIMARY KEY (`order_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COMMENT='订单表';INSERT INTO test_order (`order_id`, `order_name`) VALUES (1, '订单1');
INSERT INTO test_order (`order_id`, `order_name`) VALUES (2, '订单2');

支付表

CREATE TABLE `test_pay` (`pay_id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '支付id',`pay_name` varchar(255) NOT NULL DEFAULT '' COMMENT '支付名字',`order_id` bigint(20) NOT NULL COMMENT '订单id',PRIMARY KEY (`pay_id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 COMMENT='付款记录表';INSERT INTO test_pay (`pay_id`, `pay_name`, `order_id`) VALUES (1, '支付名字1', 1);
INSERT INTO test_pay (`pay_id`, `pay_name`, `order_id`) VALUES (2, '支付名字2', 2);

物流表（一个订单有多个阶段的物流信息）

CREATE TABLE `test_flow` (`flow_id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '物流id',`flow_begin_name` varchar(255) NOT NULL DEFAULT '' COMMENT '物流开始名字',`flow_end_name` varchar(255) NOT NULL DEFAULT '' COMMENT '物流结束名字',`order_id` bigint(20) NOT NULL COMMENT '订单id',PRIMARY KEY (`flow_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COMMENT='物流表';INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (1, '北京', '上海', 1);
INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (2, '上海', '浦东新区', 1);
INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (3, '浦东新区', '川沙新政', 1);
INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (4, '西藏', '黑龙江', 2);
INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (5, '黑龙江', '漠河', 2);
INSERT INTO test_flow (`flow_id`, `flow_begin_name`, `flow_end_name`, `order_id`) VALUES (6, '漠河', '百合路35号', 2);

1个订单对应1个支付信息
1个订单对应n个阶段的物流信息
在这里插入图片描述

存储过程

DELIMITER $$CREATE PROCEDURE `selectOrderAndFlow`(IN `orderId` bigint)
BEGINselect order_id, order_name from test_order ;
select order_id, pay_id, pay_name from test_pay ;
select order_id, flow_id, flow_begin_name, flow_end_name from test_flow ;END $$

java 文件

vo文件

package cn.fox.mydemo.domain;import lombok.Data;@Data
public class TestOrder {private Long orderId;private String orderName;}

package cn.fox.mydemo.domain;import lombok.Data;@Data
public class TestPay {/*** 支付id*/private Long payId;/*** 支付名字*/private String payName;/*** 订单id*/private Long orderId;}

package cn.fox.mydemo.domain;import lombok.Data;@Data
public class TestFlow {private static final long serialVersionUID = 1L;/*** 物流id*/private Long flowId;/*** 物流开始名字*/private String flowBeginName;/*** 物流结束名字*/private String flowEndName;/*** 订单id*/private Long orderId;}

package cn.fox.mydemo.domain.vo;import cn.fox.mydemo.domain.TestFlow;
import cn.fox.mydemo.domain.TestOrder;
import cn.fox.mydemo.domain.TestPay;
import lombok.Data;import java.util.List;@Data
public class TestOrderVo2 {/** 订单对象 */private TestOrder testOrder;/** 支付对象 */private TestPay testPay;/** 物流list */private List<TestFlow> testFlowList;}

mapper.java文件

package cn.fox.mydemo.mapper;import cn.fox.mydemo.domain.vo.TestOrderVo2;
import org.apache.ibatis.annotations.Mapper;import java.util.List;@Mapper
public interface TestOrderMapper {List<TestOrderVo2> getOrderAndFlow(Long id);}

mapper.xml文件

<?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="cn.fox.mydemo.mapper.TestOrderMapper"><resultMap type="cn.fox.mydemo.domain.vo.TestOrderVo2" id="testOrderVo2"><result property="testOrder.orderId"    column="order_id"    /><result property="testOrder.orderName"    column="order_name"    /><association property="testPay"javaType="cn.fox.mydemo.domain.TestPay"resultSet="testPay"column="order_id"foreignColumn="order_id"><id property="payId" column="pay_id"/><result property="payName" column="pay_name"/><result property="orderId" column="order_id"/></association><collection property="testFlowList"ofType="cn.fox.mydemo.domain.TestFlow"resultSet="testFlowList"column="order_id"foreignColumn="order_id"><id property="flowId" column="flow_id"/><result property="flowBeginName" column="flow_begin_name"/></collection></resultMap><select id="getOrderAndFlow"resultSets="testOrder,testPay,testFlowList"statementType="CALLABLE"resultMap="testOrderVo2">{call selectOrderAndFlow(#{id,jdbcType=INTEGER,mode=IN})}</select></mapper>

测试文件

package cn.fox.mydemo.mybatis;import cn.fox.mydemo.domain.vo.TestOrderVo2;
import cn.fox.mydemo.mapper.TestOrderMapper;
import com.alibaba.fastjson.JSONObject;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;import javax.annotation.Resource;
import java.util.List;@SpringBootTest
@RunWith(SpringRunner.class)
public class MybatisDemo2 {@Resourceprivate TestOrderMapper testOrderMapper;@Testpublic void testMybatis() {List<TestOrderVo2> orderAndFlow = testOrderMapper.getOrderAndFlow(3L);System.out.println(JSONObject.toJSONString(orderAndFlow));}}

测试结果

一次性执行3条sql，并且根据关联字段进行复杂关系映射


Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@48a46b0f] was not registered for synchronization because synchronization is not active
JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@60c96eb4] will not be managed by Spring
==>  Preparing: {call selectOrderAndFlow(?)}
==> Parameters: 3(Long)
<==    Columns: order_id, order_name
<==        Row: 1, 订单1
<==        Row: 2, 订单2
<==      Total: 2
<==    Columns: order_id, pay_id, pay_name
<==        Row: 1, 1, 支付名字1
<==        Row: 2, 2, 支付名字2
<==      Total: 2
<==    Columns: order_id, flow_id, flow_begin_name, flow_end_name
<==        Row: 1, 1, 北京, 上海
<==        Row: 1, 2, 上海, 浦东新区
<==        Row: 1, 3, 浦东新区, 川沙新政
<==        Row: 2, 4, 西藏, 黑龙江
<==        Row: 2, 5, 黑龙江, 漠河
<==        Row: 2, 6, 漠河, 百合路35号
<==      Total: 6
<==    Updates: 0
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@48a46b0f]

结果集自动映射

[{"testFlowList":[{"flowBeginName":"北京","flowEndName":"上海","flowId":1,"orderId":1},{"flowBeginName":"上海","flowEndName":"浦东新区","flowId":2,"orderId":1},{"flowBeginName":"浦东新区","flowEndName":"川沙新政","flowId":3,"orderId":1}],"testOrder":{"orderId":1,"orderName":"订单1"},"testPay":{"orderId":1,"payId":1,"payName":"支付名字1"}},{"testFlowList":[{"flowBeginName":"西藏","flowEndName":"黑龙江","flowId":4,"orderId":2},{"flowBeginName":"黑龙江","flowEndName":"漠河","flowId":5,"orderId":2},{"flowBeginName":"漠河","flowEndName":"百合路35号","flowId":6,"orderId":2}],"testOrder":{"orderId":2,"orderName":"订单2"},"testPay":{"orderId":2,"payId":2,"payName":"支付名字2"}}
]