springboot+Mybaitis 使用@mapper注解 实体类与表字段不一致

•  文章说明

在java编码过程当中变量属性通常使用驼峰命名如 
实体类属性：groupId
数据库表列：group_id 

mybatis默认是属性名和数据库字段名一一对应的，即 
数据库表列：group_id 
实体类属性：group_id 

二者有差异，在不加处理状况下，不对应字段查询时会为null，
在之前人们一般会写一大段代码来构建这种映射关系
@Results(id="id",
         value = { 
            @Result(property = "groupId", column = "group_id", id = true),
            @Result(property = "userName", column = "user_name"), 
           })

这样虽然会解决问题，可是无疑增长了代码量，下面会为你们介绍一种简便快捷的方式，来解决上述问题

•  maven引入依赖包

<dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.10</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.1</version>
        </dependency>

•  springboot连接mysql数据库

spring:
#  datasource:
#    driver-class-name: com.mysql.cj.jdbc.Driver
#    url: jdbc:mysql://localhost/test?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&useSSL=false&serverTimezone=UTC
#    username: root
#    password: root
#    hikari:
#      minimum-idle: 5
#      # 链接池最大链接数，默认是10
#      maximum-pool-size: 10
#      # 空闲链接存活最大时间，默认600000（10分钟）
#      idle-timeout: 600000
#      # 此属性控制池中链接的最长生命周期，值0表示无限生命周期，默认1800000即30分钟
#      max-lifetime: 1800000
#      # 数据库链接超时时间,默认30秒，即30000
#      connection-timeout: 30000

• java代码实体类驼峰式命名，数据库表字段以“_”分割，查询语句映射出问题解决

在yml文件中加入以下代码
mybatis:
  configuration:
    map-underscore-to-camel-case: true

• Mapper层代码

@Mapper
public interface SMapper {

    @Insert("insert into s(zname, z) values(#{zName}, #{z})")
    int insertStation(Station station);

    @Select("select * from s")
    List<S> selectAll();
}

• Service层代码

package com.service;
public interface SService {

    boolean isInsertS(S s);

    List<S> selectAllS();

}

package com.service.impl;

import java.util.List;

@Service
public class SServiceImpl implements SService {

    @Autowired
    private SMapper sMapper;

    @Override
    public boolean isInsertStationSucc(S s) {
        return sMapper.insertStation(s);
    }

    @Override
    public List<S> selectAllS() {
        List<Station> sList = sMapper.selectAll();
        return sList;
    }
}

•  Controller层代码

package com.controller;

@RestController
@RequestMapping(value = "/api", produces = {"application/json;charset=UTF-8"})  //中文乱码
@CrossOrigin //跨域
public class StationController {

    @Autowired
    private SService sService;

    @PostMapping("/selectAll")
    public List<S> selectAllS(@RequestBody String json) {
        List<S> sList = new ArrayList<>();
        try {
            sList = sService.selectAll();
        } catch (Exception e) {
            return sList;
        }
        return sList;
    }

}