准备工作

拥有 Java 开发环境以及相应 IDE，这里使用IDEA
整体框架使用 Spring Boot
项目构建使用 Maven
数据库使用MySQL
准备一张表

/*
创建用户表
*/
DROP TABLE IF EXISTS user;
CREATE TABLE user
(
id BIGINT(20) AUTO_INCREMENT NOT NULL COMMENT '主键ID',
name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
age INT(11) NULL DEFAULT NULL COMMENT '年龄',
email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
PRIMARY KEY (id)
) default charset utf8;


/*
插入测试数据
*/
INSERT INTO user (name, age, email) VALUES
('Tom', 18, 'tom@dowhere.com'),
('Jerry', 20, 'jerry@dowhere.com'),
('Aaron', 28, 'aaron@dowhere.com'),
('Jack', 21, 'jack@dowhere.com'),
('Rose', 24, 'rose@dowhere.com');

初始化工程

创建一个空的 Spring Boot 工程
提示:
可以使用 Spring Initializr 快速初始化一个 Spring Boot 工程

添加依赖
添加相关的依赖，spring-boot-starter、spring-boot-starter-test、mybatis-plus-boot-starter、lombok、MySQL 依赖，需手动添加mybatis-plus-boot-starter

		<dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.1.1</version>
        </dependency>

完整的pom

<?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 http://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>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.dowhere</groupId>
    <artifactId>mybatisplus_demo1</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mybatisplus_demo1</name>
    <description>Demo project for Spring Boot</description>

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

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

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.1.1</version>
        </dependency>

        <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>

配置

在 application.properties 配置文件中添加 MySQL数据库的相关配置

spring.datasource.driver-lass-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/test
spring.datasource.username=root
spring.datasource.password=root

编写实体类

编写实体类 User.java（我这里使用 Lombok 简化代码，IDEA中需要安装插件）

package com.dowhere.pojo;

import lombok.Data;

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

编写Mapper

编写Mapper类 UserMapper.java

package com.dowhere.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.dowhere.pojo.User;

public interface UserMapper extends BaseMapper<User> {

}

修改启动类-扫描Mapper

在 Spring Boot 启动类中添加 @MapperScan 注解，扫描 Mapper 文件夹：

测试运行

编写测试类，测试运行

package com.dowhere;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.dowhere.mapper.UserMapper;
import com.dowhere.pojo.User;
import org.junit.Assert;
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;

@RunWith(SpringRunner.class)
@SpringBootTest
public class ApplicationTests {
    @Autowired(required = false)
    private UserMapper userMapper;

    @Test
    public void selectAll() {
        System.out.println(("----- selectAll method test ------"));
        List<User> userList = userMapper.selectList(null);
        Assert.assertEquals(5, userList.size());
        userList.forEach(System.out::println);
    }

    @Test
    public void SelectById() {
        QueryWrapper  wrapper = new QueryWrapper();
        wrapper.eq("id",1);
       User user =  userMapper.selectOne(wrapper);
        System.out.println(user);
    }
}

运行结果