springboot+Mybaitis 使用@mapper註解 實體類與表字段不一致

•  文章說明

在java編碼過程當中變量屬性通常使用駝峯命名如 
實體類屬性：groupId
數據庫表列：group_id 

mybatis默認是屬性名和數據庫字段名一一對應的，即 
數據庫表列：group_id 
實體類屬性：group_id 

二者有差異，在不加處理狀況下，不對應字段查詢時會爲null，
在之前人們一般會寫一大段代碼來構建這種映射關係
@Results(id="id",
         value = { 
            @Result(property = "groupId", column = "group_id", id = true),
            @Result(property = "userName", column = "user_name"), 
           })

這樣雖然會解決問題，可是無疑增長了代碼量，下面會爲你們介紹一種簡便快捷的方式，來解決上述問題

•  maven引入依賴包

<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連接mysql數據庫

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
#      # 鏈接池最大鏈接數，默認是10
#      maximum-pool-size: 10
#      # 空閒鏈接存活最大時間，默認600000（10分鐘）
#      idle-timeout: 600000
#      # 此屬性控制池中鏈接的最長生命週期，值0表示無限生命週期，默認1800000即30分鐘
#      max-lifetime: 1800000
#      # 數據庫鏈接超時時間,默認30秒，即30000
#      connection-timeout: 30000

• java代碼實體類駝峯式命名，數據庫表字段以「_」分割，查詢語句映射出問題解決

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

• Mapper層代碼

@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層代碼

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層代碼

package com.controller;

@RestController
@RequestMapping(value = "/api", produces = {"application/json;charset=UTF-8"})  //中文亂碼
@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;
    }

}