创建表

现有一张 User 表，其表结构如下：

其对应的数据库 Schema 脚本如下：

CREATE TABLE user
(
    id BIGINT(20) 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)
);


INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, '[email protected]'),
(2, 'Jack', 20, '[email protected]'),
(3, 'Tom', 28, '[email protected]'),
(4, 'Sandy', 21, '[email protected]'),
(5, 'Billie', 24, '[email protected]');

初始化工程

创建一个空的 Spring Boot 工程

添加依赖

导入Pom配置文件

 <dependencies>
    <!--1.数据库驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    <!--2.lombok-->
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
    </dependency>
    <!--3.mybatis-plus  版本很重要3.0.5-->
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.0.5</version>
    </dependency>
    <!--4.h2-->
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
 </dependencies>

连接数据库配置

# 连接数据库
spring:
  datasource:
    username: root
    password: 123456
    url: jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8
    driver-class-name: com.mysql.cj.jdbc.Driver
  
# 设置端口号
server:
  port: 9090

编写实体类

package com.yefeng.entity;

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;
}

编写实体类对应的mapper接口

package com.yefeng.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.yefeng.entity.User;
import org.springframework.stereotype.Repository;

//在对应的接口上面继承一个基本的接口 BaseMapper
@Repository//代表持久层
public interface UserMapper extends BaseMapper<User> {
    //所有CRUD操作都编写完成了，不用像以前一样配置一大堆文件
}

在主启动类添加@MapperScan注解

package com.yefeng;

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

@MapperScan("com.yefeng.mapper")
@SpringBootApplication
public class MybaitsPlusApplication {
	public static void main(String[] args) {
		SpringApplication.run(MybaitsPlusApplication.class, args);
	}
}

进行Test测试

package com.yefeng;

import com.yefeng.entity.User;
import com.yefeng.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 MybaitsPlusApplicationTests {
     //继承了BaseMapper，所有的方法都来自父类，我们也可以编写自己的扩展方法！
	@Autowired
	private UserMapper userMapper;
	@Test
	void contextLoads() {
        //参数是一个wrapper ，条件构造器，这里我们先不用 null
		List<User> users = userMapper.selectList(null);//查询全部的用户
		for (User user : users) {
			System.out.println(user);
		}
	}

}
	

结果