mybatis-plus快速入门

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, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');

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, test1@baomidou.com, 18
<==        Row: 2, Jack, test2@baomidou.com, 20
<==        Row: 3, Tom, test3@baomidou.com, 28
<==        Row: 4, Sandy, test4@baomidou.com, 21
<==        Row: 5, Billie, test5@baomidou.com, 24
<==      Total: 5
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@50734cea]
User(id=1, name=Jone, age=18, email=test1@baomidou.com)
User(id=2, name=Jack, age=20, email=test2@baomidou.com)
User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)

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("libaitian@qq.com");
        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), libaitian@qq.com(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=libaitian@qq.com)

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。