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

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

存储过程

DELIMITER $$

CREATE PROCEDURE `selectOrderAndFlow`(IN `orderId` bigint)
BEGIN

select 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 {

    @Resource
    private TestOrderMapper testOrderMapper;

    @Test
    public 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"
        }
    }
]