Springcloud学习笔记46Mybatisplus 使用XML编写动态sql简易方法以及sql的执行顺序；

1. 入门简单案例

1.1 在Resources文件夹下创建一个Mapper文件夹

比如我们需要在User表中使用增删改查，创建PmQuartzConfigMapper.xml，对应MybatisPlus中的PmQuartzConfigMapper接口

1.2 在application.yml中配置mapper文件夹的路径

mybatis-plus:
  # xml扫描，多个目录用逗号或者分号分隔（告诉 Mapper 所对应的 XML 文件位置）
  mapper-locations: classpath:mapper/*.xml

1.3 在PmQuartzConfigMapper.java中创建函数

public interface PmQuartzConfigMapper extends BaseMapper<PmQuartzConfig> {

    // 使函数参数对应xml中的参数wxNickName
    List<PmQuartzConfig> getQuartzInfoByJobGroup(@Param("jobGroup") String jobGroup);
}

1.4 在PmQuartzConfigMapper.xml中写sql语句

<?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.ttbank.flep.mapper.PmQuartzConfigMapper">

    <select id="getQuartzInfoByJobGroup" resultType="com.ttbank.flep.entity.PmQuartzConfig">
        select * from pm_quartz_config
        where job_group=#{jobGroup}

    </select>

</mapper>

1.5 controller中调用

package com.ttbank.flep.controller;


import com.ttbank.flep.entity.PmQuartzConfig;
import com.ttbank.flep.mapper.PmQuartzConfigMapper;
import com.ttbank.flep.service.IPmQuartzConfigService;
import dto.Result;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * <p>
 *  前端控制器
 * </p>
 *
 * @author lucky
 * @since 2022-04-20
 */
@RestController
@RequestMapping("/pm-quartz-config")
public class PmQuartzConfigController {
    @Autowired
    IPmQuartzConfigService pmQuartzConfigService;

    @Autowired
    PmQuartzConfigMapper pmQuartzConfigMapper;


    @PostMapping("/getQuartzInfoByJobGroup")
    public void getQuartzInfoByJobGroup(){
        List<PmQuartzConfig> quartzConfigList = pmQuartzConfigMapper.getQuartzInfoByJobGroup("test01");
        System.out.println("");

    }

}

postman调用：

debug断点情况：

2. MyBatis Mapper XML文件详解

<?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.ttbank.flep.mapper.PmQuartzConfigMapper">
    <select id="getQuartzInfoByJobGroup" resultType="com.ttbank.flep.entity.PmQuartzConfig">
        select * from pm_quartz_config
        where job_group=#{jobGroup}

    </select>
</mapper>

 namespace 就是XXXMapper.xml文件对应的Java接口XXXMapper.java

2.1 select标签常用字段

id:填写在XxxMapper.java接口中的方法名

parameterType:填写参数的类型

resultType:填写方法中返回值的类型，直接在Idea中右键选择copy reference;

resultMap属性:与resultMap标签一起使用，填写resultMap标签中定义的id属性

2.2 resultMap标签

resultMap标签用于自定义封装结果；

type(resultMap标签中属性):最终结果还是封装到实体类中，type就是指定封装到哪一个类中
id:与<select>标签中的resultMap中的属性一直，一定要唯一

• <id>:该标签是指定主键封装到实体类中的哪一个属性(可以省略)
• <result>:该标签是其他的列封装到实体类中，一般只需填写实体类中的属性与表中列不同的项即可，property:填写实体类中的属性，column:填写表中的列名；

    <resultMap id="quartzMap" type="com.ttbank.flep.dto.QuartzDTO">
        <id property="id" column="id"/>
        <result property="jobName" column="job_name"/>
        <result property="jobGroup" column="job_group"/>
        <collection property="quartzDetailList" ofType="com.ttbank.flep.entity.PmQuartzDetail">
            <id property="id" column="bId"/>
            <result property="costTime" column="cost_time"/>
        </collection>
    </resultMap>
    <select id="getQuartzCostTime" resultMap="quartzMap">
        SELECT a.job_name, a.job_group,b.id bId,b.cost_time
        FROM pm_quartz_config a
        left join pm_quartz_detail b
        on a.job_group=b.job_group
    </select>

加一个where 条件进行限制；

pm_quartz_detail:

pm_quartz_config

 2.2 sql的执行顺序分析

sql语句定义的顺序

(1) SELECT (2)DISTINCT <select_list>
(3) FROM <left_table>
(4) <join_type> JOIN <right_table>
(5)         ON <join_condition>
(6) WHERE <where_condition>
(7) GROUP BY <group_by_list>
(8) WITH {CUBE|ROLLUP}
(9) HAVING <having_condition>
(10) ORDER BY <order_by_condition>
(11) LIMIT <limit_number>

sql语句执行顺序

(8) SELECT (9)DISTINCT<select_list>
(1) FROM <left_table>
(3) <join_type> JOIN <right_table>
(2)         ON <join_condition>
(4) WHERE <where_condition>
(5) GROUP BY <group_by_list>
(6) WITH {CUBE|ROLLUP}
(7) HAVING <having_condition>
(10) ORDER BY <order_by_list>
(11) LIMIT <limit_number>

3.Mybatis中的${}和#{}区别

https://blog.csdn.net/super_DuoLa/article/details/121971500

https://blog.csdn.net/li_w_ch/article/details/109754949

参考文献：

https://blog.csdn.net/qq_42669399/article/details/107499252

https://blog.csdn.net/qq_42780864/article/details/88055480