MyBatis-Plus，为简化开发而生，基于3.0.5版本

1：简介

        Mybatis本来就是简化JDBC操作的，而MyBatis-Plus就是简化MyBatis的，是一个 MyBatis的增强工具，在 MyBatis 的基础上只做增强不做改变，为简化开发、提高效率而生。其官网地址为：https://mp.baomidou.com/

2：快速入门

        我们将通过一个简单的 Demo 来阐述 MyBatis-Plus 的强大功能，在此之前，我们假设您已经：

• 拥有 Java 开发环境以及相应 IDE
• 熟悉 Spring Boot
• 熟悉 Maven

        创建user表

DROP TABLE IF EXISTS user;

CREATE TABLE `user` (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT '主键ID',
  `name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '姓名',
  `age` int DEFAULT NULL COMMENT '年龄',
  `email` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '邮箱',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;

        往user表插入数据

DELETE FROM user;

INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');

        创建springBoot的web项目，导入依赖

<!-- 数据库驱动的包-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>
<!-- lombok的包，为了实体类偷懒-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>
<!-- mybatis-plus的依赖，导入这个就不需要mybatis的包了-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.0.5</version>
</dependency>

        连接数据库yml配置

spring:
  datasource:
    username: root
    password: password
    url: jdbc:mysql://localhost:3306/study?userSSL=true&useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
    driver-class-name: com.mysql.cj.jdbc.Driver

        实体类User

package com.lingaolu.bean;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
   
   
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

        书写interface接口文件,继承BaseMapper，至此所有的curd已经编写我完成，就可以使用了，不需要mapper.xml文件

package com.lingaolu.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.lingaolu.bean.User;

public interface UserMapper extends BaseMapper<User> {
   
   
}

        主启动类添加扫描mapper接口的注解，根据自己目录而定

@MapperScan("com.lingaolu.mapper")

        单元测试

package com.lingaolu;

import com.lingaolu.bean.User;
import com.lingaolu.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;

@SpringBootTest
class MybatisPlusApplicationTests {
   
   

    @Autowired
    private UserMapper userMapper;
    @Test
    void contextLoads() {
   
   
        List<User> userList = userMapper.selectList(null);
        userList.forEach(System.out::println);
    }

}

        单元测试结果

3：更多操作

3-1：日志控制台输出

        想看日志的可以配置日志控制台输出

mybatis-plus:
  configuration:
    # 配置日志控制台输出
    log-impl: org.apache.ibatis.logging.stdout.StdOutImp

3-2：主键自增

        MyBatis-Plus默认的主键生成策略是IdType .ID_WORKER，使用的是雪花算法要想插入主键自增，需要

• 数据库主键设置自增
  
• 实体类添加主键自增注解
  

        其中IdType的类型有6种，其源码和注释如下

/*
 * Copyright (c) 2011-2020, hubin (jobob@qq.com).
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, eith