mybatisplus的自定义sql使用方法及VO的使用

1、根据sql的select查询语句字段来在VO包中创建对应的VO类

例如sql语句：

SELECT SUBSTRING_INDEX(CONCAT(SUBSTRING_INDEX(city,'市',1),'市'),'省',-1)as 'city',bod51 as 'inBod5',bod52 as 'outBod5' from (SELECT a.region as 'city',bod51,bod52 from sewage_plant a JOIN (select factory_name ,SUM(bod51)as 'bod51',SUM(bod52)as 'bod52' from report_form WHERE MONTH(report_time)=MONTH(CURDATE()) GROUP BY factory_name)b ON a.factory_name=b.factory_name)c

我们可以看到select出来的字段被重命名as为新字段名。则新建类相应的属性名应与此字段名相同

千万不要忘记@Data注解！！！！！！！！！！！！！！！！！！

package com.project.sewageplant3.entity.vo;

import lombok.Data;

import java.math.BigDecimal;
@Data
public class StandardSituationVO {
    private String city;
    private BigDecimal inBod5;
    private BigDecimal outBod5;
}

2、在对应的mapper层中添加注解和方法

@Repository
public interface ReportFormMapper extends BaseMapper<ReportForm> {
          
          @Select("SELECT SUBSTRING_INDEX(CONCAT(SUBSTRING_INDEX(city,'市',1),'市'),'省',-1)as 'city',bod51 as 'inBod5',bod52 as 'outBod5' from (SELECT a.region as 'city',bod51,bod52 from sewage_plant a JOIN (select factory_name ,SUM(bod51)as 'bod51',SUM(bod52)as 'bod52' from report_form WHERE MONTH(report_time)=MONTH(CURDATE()) GROUP BY factory_name)b ON a.factory_name=b.factory_name)c")
          List<StandardSituationVO> standardSituationList();
}

3、在service层的抽象类和实现类中分别添加方法

①抽象类

public List<StandardSituationVO> standardSituationList();

②抽象类的实现类（IDEA可以ctrl+o快捷添加方法）

@Override
    public List<StandardSituationVO> standardSituationList() {
        return reportFormMapper.standardSituationList(); //返回接口的方法
    }

4、最后在controller层中执行service层方法

@GetMapping("/standardSituationList")
    public List<StandardSituationVO> StandardSituationList(){
        return reportFormService.standardSituationList();  //返回service层接口方法
    }