Mybatis Plus快速入门

简介

官网：https://baomidou.com/

MyBatis-Plus 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。

愿景

我们的愿景是成为 MyBatis 最好的搭档，就像 魂斗罗 中的 1P、2P，基友搭配，效率翻倍。

（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，完全去SQL化，封装好了大量的CURD操作。 甚至把CRUD操作封装到了Service层，可以直接在controller调用现成的CRUD服务层，极度舒适省心。

局限：只支持简单的CRUD 操作。不支持多表操作（join ,union,子查询） 。

快速上手

1.建表

DROP TABLE IF EXISTS `user`;

CREATE TABLE `user`
(
id BIGINT NOT NULL COMMENT '主键ID',
name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
age INT NULL DEFAULT NULL COMMENT '年龄',
email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
PRIMARY KEY (id)
);

select * from user;

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');

<?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>3.5.9</version>
<relativePath/> &lt;!&ndash; lookup parent from repository &ndash;&gt;
</parent>–>
<groupId>com.bigdata</groupId>
<artifactId>demo1</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>demo1</name>
<description>demo1</description>
<properties>
<java.version>1.8</java.version>
<spring-cloud-alibaba.version>2.2.2.RELEASE</spring-cloud-alibaba.version>
<spring-cloud.version>Hoxton.SR8</spring-cloud.version>
<mybatis-plus.version>3.5.5</mybatis-plus.version>
<velocity.version>2.0</velocity.version>
<swagger.version>2.9.2</swagger.version>
<swagger-bootstrap-ui.version>1.9.2</swagger-bootstrap-ui.version>
<commons-lang3.version>3.9</commons-lang3.version>
<commons-fileupload.version>1.3.1</commons-fileupload.version>
<commons-io.version>2.6</commons-io.version>
<fastjson.version>1.2.28</fastjson.version>
<gson.version>2.8.6</gson.version>
<json.version>20170516</json.version>
<jodatime.version>2.10.1</jodatime.version>
<jwt.version>0.7.0</jwt.version>
<httpclient.version>4.5.1</httpclient.version>
</properties>

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.3.4.RELEASE</version>
<relativePath/> <!– lookup parent from repository –>
</parent>

<dependencies>
<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>
</dependency>
<!–mybatis-plus–>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>${mybatis-plus.version}</version>
</dependency>
<!–mybatis-plus 代码生成器–>
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-generator</artifactId>
<version>${mybatis-plus.version}</version>
</dependency>
<!– Mybatis Plus 代码生成器模板引擎, –>
<dependency>
<groupId>org.apache.velocity</groupId>
<artifactId>velocity-engine-core</artifactId>
<version>${velocity.version}</version>
</dependency>

<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</dependency>

<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>

<!– Spring Data Commons 做分页有用–>
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-commons</artifactId>
</dependency>

</dependencies>

</project>

server:
port: 8081

spring:
profiles:
active: dev
application:
name: mybatisplus-test
datasource:
driver-class-name: com.mysql.cj.jdbc.Driver
url: jdbc:mysql://127.0.0.1:3306/test?serverTimezone=GMT%2B8&characterEncoding=utf-8
username: root
password: 123456

# 打印SQL
mybatis-plus:
configuration:
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

或者如下所示：

spring.application.name=demo1
server.port=8081
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/mybatis?serverTimezone=GMT%2B8&characterEncoding=utf-8
spring.datasource.username=root
spring.datasource.password=root
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

代码生成器

虽然mybatis-plus已经节省了sql编写的大部分工作，但是当面对几十上百个表的模块处理时，仍然又大量的类模块要编写，其中最大的工作量就是实体类的编写，如果手工编写还很容易出错。

所以mybatis-plus还推出了代码生成工具。

在pom.xml中增加代码生成工具。

增加一个代码生成的工具类

CREATE TABLE `student` (
`id` int(0) NOT NULL AUTO_INCREMENT COMMENT 'ID',
`name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '姓名',
`age` int(0) NULL DEFAULT NULL COMMENT '年龄',
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;
SET FOREIGN_KEY_CHECKS = 1;

select * from student;

INSERT INTO `student` (id, name, age) VALUES
(1, '张三', 18),
(2, '李四', 20);

EasyCode 自动代码生成:

idea 连接数据库：

第一次需要下载驱动：

点击需要生成代码的表：

如果需要生成符合自己预期的代码，需要自己设置模版。

接着可以拿 teacher 表练练手：

CREATE TABLE `teacher` (
`id` int(0) NOT NULL AUTO_INCREMENT COMMENT 'ID',
`name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '姓名',
`age` int(0) NULL DEFAULT NULL COMMENT '年龄',
PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;
SET FOREIGN_KEY_CHECKS = 1;

select * from teacher;

INSERT INTO `teacher` (id, name, age) VALUES
(1, '张三', 18),
(2, '李四', 20);

条件查询

https://baomidou.com/guides/wrapper/

普通 Wrapper (QueryWrapper)：

QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.eq("name", "老王");

Lambda Wrapper (LambdaQueryWrapper)：

LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
lambdaQueryWrapper.eq(User::getName, "老王");

生成的 SQL

— 普通 Wrapper 和 Lambda Wrapper 生成的 SQL 相同
SELECT * FROM user WHERE name = '老王'

测试：查询姓名是 张开头，年龄在10到20之间的学生信息

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.bigdata.ApplicationDemo;
import com.bigdata.mapper.UserMapper;
import com.bigdata.pojo.User;

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(classes = ApplicationDemo.class)
public class ApplicationTests {

@Autowired
UserMapper userMapper;

@Test
public void test1(){
List<User> users = userMapper.selectList(null);
for (User user : users) {
System.out.println(user);
}
}

@Test
public void test2(){

/* QueryWrapper<User> queryWrapper = new QueryWrapper<>();
queryWrapper.eq("name","老王");*/

LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
//queryWrapper.eq(User::getName,"老王");
queryWrapper.lt(User::getAge,28);
queryWrapper.gt(User::getAge,18);

List<User> users = userMapper.selectList(queryWrapper);
for (User user : users) {
System.out.println(user);
}
}

}

分页查询

https://baomidou.com/guides/data-interface/#page

 狂跨

package com.demo.config;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MybatisPlusConfig {
/**
* 新增分页拦截器，并设置数据库类型为mysql
*/
@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
return interceptor;
}
}

@Test
public void testPage(){
IPage<Student> page = new Page<>(1,10);
IPage<Student> studentIPage = studentService.page(page);
List<Student> records = studentIPage.getRecords();
// 数据库中总的学生的数量
long total = studentIPage.getTotal();
System.out.println(total);
// 总共的页数
long pages = studentIPage.getPages();
System.out.println(pages);
// 每页展示多少条数据
long size = studentIPage.getSize();
System.out.println(size);

// 循环打印当前页的数据
for (Student student : records) {
System.out.println(student);
}
}

注意导入的 Page 的包为：

import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;