mybatis-plus基础使用介绍

MyBatis-Plus（简称 MP）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。
官网：mybatis-plus官网

1.创建user表及插入数据

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, '[e-mail]'), (2, 'Jack', 20, '[e-mail]'), (3, 'Tom', 28, '[e-mail]'), (4, 'Sandy', 21, '[e-mail]'), (5, 'Billie', 24, '[e-mail]'); 

2.创建一个springboot工程，导入依赖

<?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>2.2.5.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.example</groupId> <artifactId>demo</artifactId> <version>0.0.1-SNAPSHOT</version> <name>demo</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.47</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> </dependency> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.2.0</version> </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> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project> 

3.创建pojo包，新建user类

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

4.创建mapper包，新建UserMapper接口

@Repository public interface UserMapper extends BaseMapper<User> { } 

5.在application.yml中配置数据库信息

spring: datasource: username: root
    password: 123456 url: jdbc:mysql://localhost:3306/test?useSSL=false&useUnicode=true&characterEncoding=utf-8 driver-class-name: com.mysql.jdbc.Driver 

6.在主启动类添加@MapperScan(“com.mapper”)注解扫描

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

7.在测试类中测试

@SpringBootTest class DemoApplicationTests { @Autowired private UserMapper userMapper; @Test void contextLoads() { //参数Wrapper是条件构造器,null表示查看全部用户 List<User> users = userMapper.selectList(null); users.forEach(System.out::println); } } 

8.测试结果

9.配置日志
前面已经完成了快速入门，接下来配置日志。
在application.yml中添加配置

# 配置日志
mybatis-plus: configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl 

测试输出

Creating a new SqlSession SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@50734cea] was not registered for synchronization because synchronization is not active 2020-08-16 11:04:26.166 INFO 40306 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting... 2020-08-16 11:04:26.381 INFO 40306 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed. JDBC Connection [HikariProxyConnection@449966439 wrapping com.mysql.jdbc.JDBC4Connection@608eb42e] will not be managed by Spring ==> Preparing: SELECT id,name,email,age FROM user ==> Parameters: <== Columns: id, name, email, age <== Row: 1, Jone, [e-mail], 18 <== Row: 2, Jack, [e-mail], 20 <== Row: 3, Tom, [e-mail], 28 <== Row: 4, Sandy, [e-mail], 21 <== Row: 5, Billie, [e-mail], 24 <== Total: 5 Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@50734cea] User(id=1, name=Jone, age=18, email=[e-mail]) User(id=2, name=Jack, age=20, email=[e-mail]) User(id=3, name=Tom, age=28, email=[e-mail]) User(id=4, name=Sandy, age=21, email=[e-mail]) User(id=5, name=Billie, age=24, email=[e-mail]) 2020-08-16 11:04:26.439 INFO 40306 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Shutdown initiated... 2020-08-16 11:04:26.442 INFO 40306 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Shutdown completed. 2020-08-16 11:04:26.443 INFO 40306 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor' Process finished with exit code 0 

10.测试插入

@Test public void testInsert(){ User user = new User(); user.setName("haha"); user.setAge(6); user.setEmail("[e-mail]"); int insert = userMapper.insert(user);//帮我们自动生成ID System.out.println(insert); System.out.println(user);//id会自动回填 } Creating a new SqlSession SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1edac3b4] was not registered for synchronization because synchronization is not active 2020-08-16 11:15:02.161 INFO 40321 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting... 2020-08-16 11:15:02.387 INFO 40321 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed. JDBC Connection [HikariProxyConnection@1641528161 wrapping com.mysql.jdbc.JDBC4Connection@33f81280] will not be managed by Spring ==> Preparing: INSERT INTO user ( id, name, email, age ) VALUES ( ?, ?, ?, ? ) ==> Parameters: 1294835027789930497(Long), haha(String), [e-mail](String), 6(Integer) <== Updates: 1 Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@1edac3b4] 1 User(id=1294835027789930497, name=haha, age=6, email=[e-mail]) 2020-08-16 11:15:02.446 INFO 40321 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Shutdown initiated... 2020-08-16 11:15:02.450 INFO 40321 --- [extShutdownHook] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Shutdown completed. 2020-08-16 11:15:02.450 INFO 40321 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor' Process finished with exit code 0 

从上面结果，我们发现它会为我们自动生成id，数据库插入的id默认值为：全局的唯一id。

主键生成策略
分布式系统唯一id生成：分布式系统唯一id生成
雪花算法：
snowflake是Twitter开源的分布式ID生成算法，结果是一个long型的ID。其核心思想是：使用41bit作为毫秒数，10bit作为机器的ID（5个bit是数据中心，5个bit的机器ID），12bit作为毫秒内的流水号（意味着每个节点在每毫秒可以产生 4096 个 ID），最后还有一个符号位，永远是0。具体实现的代码可以参看https://github.com/twitter/snowflake。

本文地址：https://blog.csdn.net/small_apples/article/details/108033384