01、新建一个springboot项目

选择依赖和版本

SpringBoot整合lombok

lombok是一个快速生成JAVAbean的一个工具工程和生成日志的工具。未来给我们提供了很大的遍历。

需要在idea中安装插件和pom.xml中进行依赖才可以使用生效：

pom.xml依赖如下：

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>
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SpringBoot在依赖的过程，为什么有的要加版本号，有的不加？

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
    <groupId>MySQL</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.27</version>
</dependency>

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>MyBatis-plus-boot-starter</artifactId>
    <version>3.5.2</version>
</dependency>

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>
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• mysql
• mybatis-plus 都不属于springboot父工程管理，自然必须把自己的version加上去！

SpringBoot整合Mybatis-Plus和数据源

1、在pom.xml中依赖如下：

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.27</version>
</dependency>

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.2</version>
</dependency>
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2、准备一个数据库表kss_user

CREATE TABLE `kss_user` (
  `id` int NOT NULL AUTO_INCREMENT,
  `user_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_AI_ci DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `real_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
  `gender` int DEFAULT NULL,
  `birthday` date DEFAULT NULL,
  `create_time` datetime DEFAULT NULL,
  `update_time` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
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3、配置数据源和mybatis配置

在项目的resource目录下的Application.yaml配置如下：

server:
  port: 8080

# 数据源配置
spring:
  application:
    name: pug-springboot-ssm
  datasource:
    type: com.zaxxer.hikari.HikariDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://127.0.0.1:3306/ssm_db?serverTimezone=GMT%2b8&useUnicode=true&useSSL=false&characterEncoding=UTF-8
    username: root
    password: 123456
    hikari:
      connection-timeout: 60000
      validation-timeout: 3000
      idle-timeout: 60000
      login-timeout: 5
      max-lifetime: 60000
      maximum-pool-size: 30
      minimum-idle: 10
      read-only: false


# mybatis-plus配置
mybatis-plus:
  configuration:
    log-impl: org.Apache.ibatis.logging.stdout.StdOutImpl
  mapper-locations:
    - classpath*:/mapper/*.xml
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4、在resource新建一个mapper文件用来存放mybatis的xml文件

5、springboot整合mybatis-plus

package com.ksd.pug;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.ksd.pug.mapper")
public class PugSpringbootSsmApplication {

    public static void main(String[] args) {
        SpringApplication.run(PugSpringbootSsmApplication.class, args);
    }

}
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SpringBoot实现对用户表的CRUD操作

01、pojo

package com.ksd.pug.pojo;

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;
import lombok.ToString;

import java.io.Serializable;
import java.util.Date;

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
@TableName("kss_user")
public class User implements Serializable {

    @TableId(type = IdType.AUTO)
    private Integer id;
    private String username;
    private String password;
    private String realName;
    private Integer gender;
    private Date birthday;

}
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02、mapper

package com.ksd.pug.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.ksd.pug.pojo.User;

public interface UserMapper extends BaseMapper<User> {
}
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03、service和serviceImpl

package com.ksd.pug.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.ksd.pug.pojo.User;

public interface IUserService extends IService<User> {
}
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package com.ksd.pug.service;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.ksd.pug.mapper.UserMapper;
import com.ksd.pug.pojo.User;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;

@Slf4j
@Service
public class IUserServiceImpl extends ServiceImpl<UserMapper, User> implements IUserService {
}
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04、controller

package com.ksd.pug.controller;


import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.ksd.pug.config.exception.BusinessException;
import com.ksd.pug.config.results.Code;
import com.ksd.pug.config.results.Result;
import com.ksd.pug.pojo.User;
import com.ksd.pug.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/user")
public class UserController {

    @Autowired
    private IUserService userService;

    @PostMapping
    public Result save(User user){
        boolean flag = userService.saveOrUpdate(user);
        return new Result(flag ? Code.SAVE_OK:Code.SAVE_ERROR);
    }

    @PutMapping
    public Result update(User user){
        boolean flag = userService.updateById(user);
        return new Result(flag ? Code.UPDATE_OK:Code.UPDATE_ERROR);
    }

    @DeleteMapping("/{id}")
    public Result delete(Integer id){
        boolean flag = userService.removeById(id);
        return new Result(flag ? Code.DELETE_OK:Code.DELETE_ERROR);
    }

    @GetMapping("/{id}")
    public Result get(@PathVariable("id")Integer id) throws BusinessException {
        User user = userService.getById(id);
        // 模拟出现异常，使用条件控制，便于测试结果
        if (id == 10) {
            throw new BusinessException("查询出错了，请重试！",Code.GET_ERROR);
        }
        return new Result(null != user ? Code.GET_OK :Code.GET_ERROR,user);
    }

    @GetMapping("/{pageNo}/{pageSize}")
    public Result getAll(@PathVariable Integer pageNo,@PathVariable Integer pageSize){
        // 1、设置分页
        Page page = new Page<>(pageNo,pageSize);
        // 2、设置条件
        LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
        // 3、查询分页返回
        IPage page1 = userService.page(page, lambdaQueryWrapper);
        return new Result(null != page1 ? Code.GET_OK :Code.GET_ERROR,page1);
    }


}
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Mybatis-Plus的分页失效问题

@Configuration
public class MybatisPlusConfig {

    /**
     * 新的分页插件,一缓和二缓遵循mybatis的规则,需要设置 MybatisConfiguration#useDeprecatedExecutor = false 避免缓存出现问题(该属性会在旧插件移除后一同移除)
     */

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}
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Mybatis-Plus的创建时间和更新时间回填问题

1. 定义个回填配置类

@Slf4j
@Component 
public class MyMetaObjectHandler implements MetaObjectHandler {

    @Override
    public void insertFill(MetaObject metaObject) {
        log.info("start insert fill...");
        //default MetaObjectHandler setFieldValByName(String fieldName, Object fieldVal, MetaObject metaObject)
        this.setFieldValByName("createTime",new Date(),metaObject);
        this.setFieldValByName("updateTime",new Date(),metaObject);

    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
}
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2. 在pojo中使用@TableFiled(fill=xxx)指定回填触发方法

package com.ksd.pug.pojo;

import com.baomidou.mybatisplus.annotation.*;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.io.Serializable;
import java.util.Date;

@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
@TableName("kss_user")
public class User implements Serializable {

    @TableId(type = IdType.AUTO)
    private Integer id;
    private String userName;
    private String password;
    private String realName;
    private Integer gender;
    private Date birthday;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;

}
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数据库级别的解决方案

首先将字段设置为timestamp，然后设置不是null，根据当前时间戳更新，在这里注意我们的create_time是不根据当前时间戳更新的！这种方式虽然可以但是不建议！

在mysql低版本的时候可能会出现一个问题，你的sql语句无法导入，而导致这个的原因是有的他只可以设置一个timestamp（在这里提示：mysql5.7 、mysql8.0是可以的！）

Mybatis-Plus是怎么做到不写sql但是可以实现CRUD操作

• 背后绝对是拼接SQL语句，然后调用mybatis底层执行sql。

具体需要学习mp！

作者：Nakano_May
链接：
https://juejin.cn/post/7183739358883610680