1.创建数据库及表

1.1.创建mp库

1.2.创建user表，建表语句如下：

CREATE TABLE `user` (
  `id` bigint(20) NOT NULL COMMENT '主键',
  `name` varchar(30) DEFAULT NULL COMMENT '姓名',
  `age` int(11) DEFAULT NULL COMMENT '年龄',
  `email` varchar(50) DEFAULT NULL COMMENT '邮箱',
  `manager_id` bigint(20) DEFAULT NULL COMMENT '直属上级id',
  `create_time` datetime DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`id`),
  KEY `manager_fk` (`manager_id`),
  CONSTRAINT `manager_fk` FOREIGN KEY (`manager_id`) REFERENCES `user` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

1.3.添加如下测试数据：

insert into `user` (`id`, `name`, `age`, `email`, `manager_id`, `create_time`) values('1087982257332887553','大boss','40','boss@baomidou.com',NULL,'2019-01-11 14:20:20');
insert into `user` (`id`, `name`, `age`, `email`, `manager_id`, `create_time`) values('1088248166370832385','王天风','25','wtf@baomidou.com','1087982257332887553','2019-02-05 11:12:22');
insert into `user` (`id`, `name`, `age`, `email`, `manager_id`, `create_time`) values('1088250446457389058','李艺伟','28','lyw@baomidou.com','1088248166370832385','2019-02-14 08:31:16');
insert into `user` (`id`, `name`, `age`, `email`, `manager_id`, `create_time`) values('1094590409767661570','张雨琪','31','zjq@baomidou.com','1088248166370832385','2019-01-14 09:15:15');
insert into `user` (`id`, `name`, `age`, `email`, `manager_id`, `create_time`) values('1094592041087729666','刘红雨','32','lhm@baomidou.com','1088248166370832385','2019-01-14 09:48:16');

2.创建maven项目

2.1.添加如下依赖

pom.xml文件内容：

<?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>2.1.8.RELEASE</version>
        <relativePath/> 
    </parent>
    <groupId>com.mp</groupId>
    <artifactId>mybatisplus</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mybatisplus</name>
    <description>mybatisplus</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!-- springboot web启动器 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- mysql jdbc驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <!-- lombok简化java代码 -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <scope>provided</scope>
        </dependency>
        <!-- mybatis-plus启动器 -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.2.0</version>
        </dependency>
        <!-- commons-lang3 -->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.9</version>
        </dependency>
        <!-- springboot test启动器 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2.2.在resources包下添加配置文件

application.yml配置文件内容：

server:
  port: 8088
  
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/MP?characterEncoding=utf8&useSSL=false&serverTimezone=GMT%2B8
    username: root
    password: 123456

2.3.创建启动类

package com.mp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @Description 启动类
 * @Author LL
 * @Date 2020-03-22 12:21
 */
@MapperScan("com.mp.dao")
@SpringBootApplication
public class MpApplication {
    public static void main(String[] args) {
        SpringApplication.run(MpApplication.class, args);
    }
}

2.4.创建实体类

package com.mp.entity;
import lombok.Data;
import java.time.LocalDateTime;

/**
 * @Description 实体类
 * @Author LL
 * @Date 2020-03-22 12:22
 */
@Data
public class User {

    private Long id;//主键
    private String name;//姓名
    private Integer age;//年龄
    private String email;//邮箱
    private Long managerId;//上级id
    private LocalDateTime createTime;//创建时间
    
}

2.5.创建dao接口

package com.mp.dao;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mp.entity.User;

/**
 * @Description 数据访问层
 * @Author LL
 * @Date 2020-03-22 12:31
 */
public interface UserMapper extends BaseMapper<User> {
}

3.编写测试类测试结果

3.1.测试类

package com.mp;

import com.mp.dao.UserMapper;
import com.mp.entity.User;
import org.junit.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;

import java.util.List;

/**
 * @Description 测试类
 * @Author LL
 * @Date 2020-03-22 12:35
 */
@SpringBootTest
@RunWith(SpringRunner.class)
public class SimpleTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void select(){
        List<User> users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }

}

3.2.测试结果