MyBatis-Plus Overview and Getting Started

1. Introduction

What is it? MyBatis is meant to simplify JDBC operations! Simplify MyBatis!

Official website
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2. Features

No intrusion : only enhance and do not change, the introduction of it will not affect the existing project, it is silky smooth
Low loss : basic CURD will be automatically injected at startup, performance is basically no loss, direct object-oriented operation
Powerful CRUD operations : built-in general Mapper and general Service, only a small amount of configuration can realize most of the CRUD
operations of a single table , and a more powerful condition builder to meet various usage needs
Support Lambda form call : through Lambda expressions, you can easily write all kinds of query conditions, no need to worry about writing wrong fields
Supports automatic primary key generation : supports up to 4 primary key strategies (including a distributed unique ID generator-Sequence), which can be configured freely, which perfectly solves the primary key problem
Support ActiveRecord mode : Support ActiveRecord form call, entity classes only need to inherit Model class to perform powerful CRUD
operations
Support custom global general operations : support global general method injection (Write once, use anywhere)
Built-in code generator : Use code or Maven plug-in to quickly generate Mapper, Model, Service, Controller
layer code, support template engine, and more custom configurations for you to use
Built-in paging plug-in : Based on MyBatis physical paging, developers do not need to care about specific operations. After configuring the plug-in, writing paging is equivalent to ordinary List query
Paging plugin supports multiple databases : supports MySQL, MariaDB, Oracle, DB2, H2, HSQL, SQLite, Postgre, SQLServer and other databases
Built-in performance analysis plug-in : Sql statement and its execution time can be output. It is recommended to enable this function during development and testing to quickly detect slow queries
Built-in global interception plug-in : Provides intelligent analysis and blocking of delete and update operations of the entire table, and can also customize interception rules to prevent misoperations

Three, quick start

Address: https://mp.baomidou.com/guide/quick-start.html Initialization project

Steps:
1. Create the database mybatis_plus
2. Create the user table

DROP TABLE IF EXISTS user;

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)
);

DELETE FROM user;

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]');
-- 真实开发中，version（乐观锁）、deleted（逻辑删除）、gmt_create、gmt_modified

3. Write the project and initialize the project! Use SpringBoot to initialize!
4. Import dependencies

SpringBoot：

<!-- 数据库驱动 --> 
         <dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<scope>runtime</scope>
		</dependency>
		<!-- mybatis-plus --> <!-- mybatis-plus 是自己开发，并非官方的！ --> 
		<dependency>
			<groupId>com.baomidou</groupId>
			<artifactId>mybatis-plus-boot-starter</artifactId>
			<version>3.4.2</version>
		</dependency>
	<!-- lombok -->
		<dependency>
			<groupId>org.projectlombok</groupId>
			<artifactId>lombok</artifactId>
			<version>1.18.16</version>
			<scope>provided</scope>
		</dependency>

SpringMVC

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus</artifactId>
    <version>3.4.2</version>
</dependency>

注意: We use mybatis-plus to save us a lot of code. After introducing MyBatis-Plus, please do not introduce MyBatis and MyBatis-Spring again to avoid problems caused by version differences.

5. Connect to the database! This step is the same as mybatis!

# mysql 5  驱动不同 com.mysql.jdbc.Driver
# mysql 8  驱动不同com.mysql.cj.jdbc.Driver、需要增加时区的配置  serverTimezone=GMT%2B8
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mybatisplus?useSSl=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=GMT%2B8
    username: root
    password: "081020"
    driver-class-name: com.mysql.cj.jdbc.Driver

Traditional way domain-dao (connect to mybatis, configure mapper.xml file)-service-controller

6. After using mybatis-plus

domain

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

mapper interface

// 在对应的Mapper上面继承基本的类 BaseMapper 
@Repository // 代表持久层 
public interface Usermapper extends BaseMapper<User> {
    
    
 // 所有的CRUD操作都已经编写完成了   
  // 你不需要像以前的配置一大堆文件了
}

注意: We need to scan all interfaces under our mapper package on the main startup class @MapperScan("com.latte.mapper")

Test in the test class

@Autowired
 // 继承了BaseMapper，所有的方法都来自己父类    
 // 我们也可以编写自己的扩展方法！ 
	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 
	   // 查询全部用户 
		List<User> users = usermapper.selectList(null);
		for (User user : users) {
    
    
			System.out.println(user);
		}
	}

result

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1. Who helped us write SQL? MyBatis-Plus has been written

2. Where did the method come from? MyBatis-Plus has been written

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