前言

发现项目框架是MybatisPlus的，由于个人使用该框架的CRUD比较少
对此学习过程中，从零到有开始搭建学习还是比较重要的，感悟会比较多

关于各个类的使用，可看如下文章：

1. 剖析Java中的Entity、service、serviceImpl、Mapper以及Controller层之间的关系（代码诠释）
2. 区分JAVA项目中的ENTITY，VO，DTO，BO

1. 搭建项目

为了更好展示
在数据库中设计一张表，并且在表格中添加数据（数据和表格名称具体看个人实操）：

其中主键id需要设置自增！

其内容具体如下所示：

在代码模块中，搭建基本的spring项目（由于现有的springboot模块比较新，不好兼容，对此需要对pom文件进行修改）：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.6.15</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.example</groupId><artifactId>demo</artifactId><version>0.0.1-SNAPSHOT</version><name>demo</name><description>demo</description><properties><java.version>21</java.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>2.3.0</version></dependency><dependency><groupId>com.mysql</groupId><artifactId>mysql-connector-j</artifactId><scope>runtime</scope></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter-test</artifactId><version>2.3.0</version><scope>test</scope></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.3.1</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><scope>test</scope></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId><configuration><image><builder>paketobuildpacks/builder-jammy-base:latest</builder></image></configuration></plugin></plugins><resources><resource><directory>src/main/java</directory><includes><include>**/*.xml</include></includes><filtering>false</filtering></resource></resources></build></project>

并且配置好数据库文件：

server.port=8081
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/blade_test?useSSL=false&useUnicode=true&characterEncoding=utf-8&zeroDateTimeBehavior=convertToNull&transformedBitIsBoolean=true&tinyInt1isBit=false&allowMultiQueries=true&serverTimezone=GMT%2B8&allowPublicKeyRetrieval=true
spring.datasource.username=root
spring.datasource.password=root

主体的项目文件如下所示：

启动类如下所示：

package com.example.demo;import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@MapperScan("com.example.demo.mapper")
@SpringBootApplication
public class DemoApplication {public static void main(String[] args) {SpringApplication.run(DemoApplication.class, args);}}

其中User实体类如下所示：

package com.example.demo.entity;import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
//@AllArgsConstructor
//@NoArgsConstructor
@TableName("test_user")
public class User {@TableId(type = IdType.AUTO)private int id;private String username;private String password;// 其他字段...
}

对应的Mapper类如下所示：

package com.example.demo.mapper;import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.entity.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;@Mapper
public interface UserMapper extends BaseMapper<User> {// 这里可以自定义一些查询方法
}

其Service类如下所示：

package com.example.demo.service;import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.entity.User;public interface UserService extends IService<User> {// 这里可以自定义一些业务方法
}

Serviceimpl类如下所示：

package com.example.demo.service.impl;import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.entity.User;
import com.example.demo.mapper.UserMapper;
import com.example.demo.service.UserService;
import org.springframework.stereotype.Service;@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {// 这里可以实现自定义的业务方法
}

为了方便测试可以写一个Springboot的测试类：（其包名一定要对应一致）：

package com.example.demo;import com.example.demo.entity.User;
import com.example.demo.mapper.UserMapper;
import com.example.demo.service.UserService;
import org.junit.jupiter.api.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;@RunWith(SpringRunner.class)
@SpringBootTest(classes = DemoApplication.class)class DemoApplicationTests {@AutowiredUserMapper userMapper;@AutowiredUserService userService;

2. 基本的CRUD

可以再controller中写入方法，并测试其接口。也可直接再测试类中输入，有可观的输出

类似Controller类中：

package com.example.demo.controller;import com.example.demo.entity.User;
import com.example.demo.mapper.UserMapper;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;@RestController
@RequestMapping("/user")
public class UserController {@Autowiredprivate UserService userService;@Autowiredprivate UserMapper userMapper;@GetMapping("/select")public User getUserById() {User user = userMapper.selectById(1);return user;}@GetMapping("/{id}")public User getUserById(@PathVariable int id) {return userService.getById(id);}@PostMapping("/add")public String addUser(@RequestBody User user) {userService.save(user);return "User added successfully!";}@PutMapping("/update")public String updateUser(@RequestBody User user) {userService.updateById(user);return "User updated successfully!";}@DeleteMapping("/delete/{id}")public String deleteUser(@PathVariable int id) {userService.removeById(id);return "User deleted successfully!";}
}

通过接口进行测试，具体如下：

或者直接再测试类：

    @Testpublic void TestSelectById(){User user = userMapper.selectById(1);System.out.println(user);}

结果如下:

又比如测试类中的这些CRUD方法：（诸如其他，各位博友可自行尝试）：

    @Testpublic void getUserById() {List<User> one = userMapper.selectList(Wrappers.<User>lambdaQuery().eq(User::getUsername,"manong"));System.out.println(one);}

截图如下：

其中service以及mapper都有其各自的方法进行CRUD