SpringBoot+MybatisPlus+Mysql小冒险
0 前提
- 安装了MySQL
- 一款适合自己的开发环境
1 数据库准备
创建数据库和表格
创建数据库的SQL语句如下：
CREATE DATABASE springboottestuser;创建表格的SQL语句如下：
DROP TABLE IF EXISTS `t_user`;
CREATE TABLE `t_user` (
`id` int(20) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`sex` varchar(10) DEFAULT NULL,
`score` varchar(20) DEFAULT NULL,
`age` int(3) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of t_user
-- ----------------------------
INSERT INTO `t_user` VALUES ('1', 'cll', 'nan', '120', '20');
INSERT INTO `t_user` VALUES ('2', 'xc', 'nan', '20', '80');
INSERT INTO `t_user` VALUES ('3', 'kl', 'nv', '60', '20');
INSERT INTO `t_user` VALUES ('4', 'ok', 'nv', '80', '24');数据准备完毕
2 Springboot相关
2.1 构建Springboot项目
在网址为https://start.spring.io/的网页里，进行选择后，下载压缩包
完成初始化项目
2.2 编写代码
要测试的数据库为
项目结构如下图：
pom.xml文件如下：
4.0.0
org.springframework.boot
spring-boot-starter-parent
2.1.3.RELEASE
com.example
sbtMybatisP
0.0.1-SNAPSHOT
sbtMybatisP
Demo project for Spring Boot
11
org.springframework.boot
spring-boot-starter
mysql
mysql-connector-java
runtime
org.springframework.boot
spring-boot-starter-web
org.projectlombok
lombok
true
org.springframework.boot
spring-boot-starter-test
test
com.baomidou
mybatis-plus-boot-starter
3.1.0
org.springframework.boot
spring-boot-maven-plugin
pom.xml文件中关于mybatisPlus的依赖是在mvn repository中查询后添加的。
添加mapper和entity后，项目结构如下
数据库配置文件application.properties如下：
密码处填自己数据库的密码
URL中3306/后填自己的数据库
jdbc.type=mysql
spring.datasource.url=jdbc:mysql://localhost:3306/springboottestuser?useUnicode=true&\
characterEncoding=utf8&serverTimezone=UTC
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=123
//实例代码
package com.example.sbtMybatisP.entity;
import lombok.Data;
@Data
public class T_User {
private Integer id;
private String name;
private String sex;
private String score;
private Integer age;
}
//UserMapper文件
package com.example.sbtMybatisP.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.sbtMybatisP.entity.T_User;
public interface UserMapper extends BaseMapper{
}
主启动程序
package com.example.sbtMybatisP;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
@MapperScan("com.example.sbtMybatisP.mapper")
public class SbtMybatisPApplication {
public static void main(String[] args) {
SpringApplication.run(SbtMybatisPApplication.class, args);
}
}
测试代码
package com.example.sbtMybatisP;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import com.example.sbtMybatisP.entity.T_User;
import com.example.sbtMybatisP.mapper.UserMapper;
import java.util.List;
import javax.annotation.Resource;
@RunWith(SpringRunner.class)
@SpringBootTest
public class SbtMybatisPApplicationTests {
@Test
public void contextLoads() {
}
@Resource
private UserMapper um;
@Test
public void testSelect(){
System.out.println("-begin select-");
List user = um.selectList(null);
user.forEach(System.out::println);
}
}
运行测试代码即可。
出现以下异常
org.springframework.jdbc.BadSqlGrammarException:
### Error querying database. Cause: java.sql.SQLSyntaxErrorException: Table 'springboottestuser.t__user' doesn't exist
### The error may exist in com/example/sbtMybatisP/mapper/UserMapper.java (best guess)
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: SELECT id,name,sex,score,age FROM t__user
### Cause: java.sql.SQLSyntaxErrorException: Table 'springboottestuser.t__user' doesn't exist
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: Table 'springboottestuser.t__user' doesn't exist说明表名是错的，改成T_user,得到以下结果
-begin select-
T_user(id=1, name=cll, sex=nan, score=120, age=20)
T_user(id=2, name=xc, sex=nan, score=20, age=80)
T_user(id=3, name=kl, sex=nv, score=60, age=20)
T_user(id=4, name=ok, sex=nv, score=80, age=24)完成！
3 总结
刚开始在启动程序中MapperScan()直接写到了具体的mapper文件，所以失败了
路漫漫其修远兮，继续学习