[Java知识库]mybatis-plus快速上手

快速入门

官网文档也有入门介绍，如果有耐心和一定基础的小伙伴可以直接看官网传送门

准备依赖

1.mybatis-plus依赖

<dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.3</version>
</dependency>

2.mysql驱动JDBC依赖

<dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
</dependency>
<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

3.mysql驱动、JDBC和其他springboot依赖可以在IDEA中构建springboot项目时选择添加，这里就不加概述。

准备数据

创建user表

DROP DATABASE IF EXISTS mybatis_plus;

CREATE DATABASE mybatis_plus;

USE mybatis_plus;

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',
    create_time DATETIME COMMENT '创建时间',
    update_time DATETIME COMMENT '更新时间',
    PRIMARY KEY (id)
);

DELETE FROM user where 1 = 1;

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');

初始化工程

用IDEA初始化一个springboot项目

配置数据源

在resource目录下的配置文件里配置自己的数据源，建议在application.yml中配置

spring:
  datasource:
    username: root
    password: nihao123
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis_plus?useSSL=true&useUnicode=true&characterEcoding=utf-8
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

注意，我这里使用的mysql驱动是8+，在url中还需要配置时区，因为我在mysql配置文件中设置了默认时区，所以这里我没有配置时区。如果没有设置时区请加上serverTimezone=Asia/Shanghai.

另外，如果mysql驱动用的5+版本则应这样driver-class-name: com.mysql.jdbc.Driver配置驱动。

下面的mybatis-plus配置是开启日志，因为我没有导入其他的日志依赖，所以用的是自带的日志

创建User实体类

在pojo包下创建User对象，这里我引入了Lombok，用Lombok给对象创建构造器以及getter和setter

注意：若之前在IDEA中并未使用过Lombok，请先在IDEA中安装Lombok插件，Lombok

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.util.Date;

@ToString //重写toString方法
@AllArgsConstructor //创建有参构造
@Data //创建getter和setter
@NoArgsConstructor //创建无参构造，用了创建有参构造的注解是默认没有无参构造的，需要手动创建
public class User {
    @TableId(type = IdType.AUTO) //主键注解，具体参考官方文档，注意使用AUTO创建表时请把主键设置为自增
    private long id;
    private String name;
    private int age;
    private String email;

    @TableField(fill = FieldFill.INSERT)//字段注解，具体参考官方文档
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
}

这里的@TableField后面会讲到,可以先暂时跳过

配置Mybatis-Plus

在main/src目录下创建mapper文件夹，在mapper文件夹下创建UserMapper这个接口，让这个接口继承BaseMapper ,注意泛型里面是要操作的实体类

package com.mybatis_plus.Mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mybatis_plus.pojo.User;
import org.springframework.stereotype.Repository;

//@Repository
@Mapper//一般就是用这个注解了
public interface UserMapper extends BaseMapper<User> {
	//这里可以自己写sql，用法和mybatis一样。现在暂时不写，仅测试mybatis-plus的实现类
}

然后还要在springboot启动类上添加扫描注解，扫描这个mapper

注意：扫描包名千万别写错了，否则后面的代码全部白写

package com.mybatis_plus;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

//@MapperScan("com.mybatis_plus.Mapper")如果mapper层注释为repository就加一个这个注解
@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

测试

在spring boot测试类里面编写测试类

查询

查询所有用户

package com.mybatis_plus;

import com.mybatis_plus.Mapper.UserMapper;
import com.mybatis_plus.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
class DemoApplicationTests {

    @Autowired
    UserMapper userMapper;
    @Test
    void contextLoads() {
        List<User> users = userMapper.selectList(null);//这里的参数是一个条件构造器wrapper,这里先暂时不讲，后面会讲到
        users.forEach(System.out::println);
    }
}

运行测试，得到结果(因为开启了日志，所以在控制台看到了sql这个执行过程,因为我之前测试过，所以表里的数据有些不一样)

控制台输出:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.6.4)

2022-03-12 14:27:54.068  INFO 9548 --- [           main] com.feng.MybatisplusApplicationTests     : Starting MybatisplusApplicationTests using Java 1.8.0_202 on SmallWolfberry with PID 9548 (started by 冯小强 in E:\Java\springboot\mybatisplus)
2022-03-12 14:27:54.069  INFO 9548 --- [           main] com.feng.MybatisplusApplicationTests     : No active profile set, falling back to 1 default profile: "default"
Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
Property 'mapperLocations' was not specified.
 _ _   |_  _ _|_. ___ _ |    _ 
| | |\/|_)(_| | |_\  |_)||_|_\ 
     /               |         
                        3.4.3 
This primary key of "id" is primitive !不建议如此请使用包装类 in Class: "com.feng.entity.User"
2022-03-12 14:27:56.229  INFO 9548 --- [           main] com.feng.MybatisplusApplicationTests     : Started MybatisplusApplicationTests in 2.544 seconds (JVM running for 3.685)

Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@350a94ce] was not registered for synchronization because synchronization is not active
2022-03-12 14:27:56.449  INFO 9548 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2022-03-12 14:27:57.551  INFO 9548 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
JDBC Connection [HikariProxyConnection@488422671 wrapping com.mysql.cj.jdbc.ConnectionImpl@6fa13e6] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,create_time,update_time FROM user
==> Parameters: 
<==    Columns: id, name, age, email, create_time, update_time
<==        Row: 1, Jone, 18, test1@baomidou.com, null, null
<==        Row: 2, Jack, 20, test2@baomidou.com, null, null
<==        Row: 3, Tom, 28, test3@baomidou.com, null, null
<==        Row: 4, Sandy, 21, test4@baomidou.com, null, null
<==        Row: 5, Billie, 24, test5@baomidou.com, null, null
<==      Total: 5
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@350a94ce]
User(id=1, name=Jone, age=18, email=test1@baomidou.com, createTime=null, updateTime=null)
User(id=2, name=Jack, age=20, email=test2@baomidou.com, createTime=null, updateTime=null)
User(id=3, name=Tom, age=28, email=test3@baomidou.com, createTime=null, updateTime=null)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com, createTime=null, updateTime=null)
User(id=5, name=Billie, age=24, email=test5@baomidou.com, createTime=null, updateTime=null)

2022-03-12 14:27:57.631  INFO 9548 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-03-12 14:27:57.633  INFO 9548 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Process finished with exit code 0

除此之外，除了selectList（）方法以外，mybatis-plus还带有很多其他的查询方法方法，在此不一一演示

，读者可以自行探索

使用Service层来调用服务:

准备工作:

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新建一个UserService类:

package com.feng.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.feng.entity.User;

/**
 * @Description:
 * @Author Ladidol
 * @Date: 2022/3/12 14:55
 * @Version 1.0
 */

public interface UserService extends IService<User> {
    Boolean saveUser() throws Exception;
}

新建一个UserServiceImpl实现类:

package com.feng.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.feng.entity.User;
import com.feng.mapper.UserMapper;
import com.feng.service.UserService;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;

/**
 * @Description:
 * @Author Ladidol
 * @Date: 2022/3/12 14:55
 * @Version 1.0
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User>   implements UserService {

    @Override
    public Boolean saveUser() throws Exception {
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<User>()
                .eq(User::getId, 6)
                .eq(User::getName, "ladidol")
                .eq(User::getEmail, "599426945@qq.com");
        User oldUser = baseMapper.selectOne(queryWrapper);
        if (!StringUtils.isEmpty(oldUser)) {
            throw new Exception();
        }
        User newUser = new User();
        newUser.setAge(20);
        newUser.setName("ladidol");
        newUser.setEmail("ladidol@outlook.com");
        return baseMapper.insert(newUser) > 0;

    }
}

测试类中新添加方法:

package com.feng;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.feng.entity.User;
import com.feng.service.UserService;
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
class MybatisplusApplicationTests {


    @Autowired
    BaseMapper<User> baseMapper;

    @Autowired
    UserService userService;

    @Test
    void contextLoads() {
        List<User> users = baseMapper.selectList(null);//这里的参数是一个条件构造器wrapper,这里先暂时不讲，后面会讲到
        users.forEach(System.out::println);
    }


    @Test
    void saveTest() throws Exception {
        userService.saveUser();

    }
}

运行结果:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.6.4)

2022-03-12 15:06:39.024  INFO 14752 --- [           main] com.feng.MybatisplusApplicationTests     : Starting MybatisplusApplicationTests using Java 1.8.0_202 on SmallWolfberry with PID 14752 (started by 冯小强 in E:\Java\springboot\mybatisplus)
2022-03-12 15:06:39.025  INFO 14752 --- [           main] com.feng.MybatisplusApplicationTests     : No active profile set, falling back to 1 default profile: "default"
Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
Property 'mapperLocations' was not specified.
 _ _   |_  _ _|_. ___ _ |    _ 
| | |\/|_)(_| | |_\  |_)||_|_\ 
     /               |         
                        3.4.3 
2022-03-12 15:06:41.136  INFO 14752 --- [           main] com.feng.MybatisplusApplicationTests     : Started MybatisplusApplicationTests in 2.669 seconds (JVM running for 3.816)

Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@790a251b] was not registered for synchronization because synchronization is not active
2022-03-12 15:06:41.387  INFO 14752 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2022-03-12 15:06:42.509  INFO 14752 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
JDBC Connection [HikariProxyConnection@1134011961 wrapping com.mysql.cj.jdbc.ConnectionImpl@24841372] will not be managed by Spring
==>  Preparing: SELECT id,name,age,email,create_time,update_time FROM user WHERE (id = ? AND name = ? AND email = ?)
==> Parameters: 6(Integer), ladidol(String), 599426945@qq.com(String)
<==      Total: 0
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@790a251b]
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@47406941] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@1643565953 wrapping com.mysql.cj.jdbc.ConnectionImpl@24841372] will not be managed by Spring
==>  Preparing: INSERT INTO user ( name, age, email, create_time, update_time ) VALUES ( ?, ?, ?, ?, ? )
==> Parameters: ladidol(String), 20(Integer), ladidol@outlook.com(String), null, null
<==    Updates: 1
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@47406941]

2022-03-12 15:06:42.596  INFO 14752 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2022-03-12 15:06:42.599  INFO 14752 --- [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

代码自动生成器

mybatis-plus可以通过代码自动生成代码

需要导入如下依赖:

<dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-generator</artifactId>
            <version>3.4.1</version>
</dependency>
<dependency>
            <groupId>org.apache.velocity</groupId>
            <artifactId>velocity-engine-core</artifactId>
            <version>2.3</version>
</dependency>

编写运行程序代码:

package com.feng;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.generator.AutoGenerator;
import com.baomidou.mybatisplus.generator.config.*;
import com.baomidou.mybatisplus.generator.config.po.TableFill;
import com.baomidou.mybatisplus.generator.config.rules.DateType;
import com.baomidou.mybatisplus.generator.config.rules.NamingStrategy;
import java.util.ArrayList;

// 演示例子，执行 main 方法控制台输入模块表名回车自动生成对应项目目录中
public class CodeGenerator {
    public static void main(String[] args) {
        // 需要构建一个 代码自动生成器 对象
        AutoGenerator mpg = new AutoGenerator();
// 配置策略
// 1、全局配置
        GlobalConfig gc = new GlobalConfig();
        String projectPath = System.getProperty("user.dir");//用户当前的目录,可以根据需求改
        gc.setOutputDir(projectPath+"/src/main/java");//配置输出路径
        gc.setAuthor("Ladidol");//配置作者
        gc.setOpen(false);
        gc.setFileOverride(false); // 是否覆盖
        gc.setServiceName("%sService"); // 去Service的I前缀
        gc.setIdType(IdType.AUTO);
        gc.setDateType(DateType.ONLY_DATE);
        gc.setSwagger2(true);
        mpg.setGlobalConfig(gc);
//2、设置数据源
        DataSourceConfig dsc = new DataSourceConfig();
        dsc.setUrl("jdbc:mysql://localhost:3306/mybatis_plus?useSSL=true&useUnicode=true&characterEcoding=utf-8");//配置数据库url
        dsc.setDriverName("com.mysql.cj.jdbc.Driver");
        dsc.setUsername("root");//用户
        dsc.setPassword("nihao123");//密码
        dsc.setDbType(DbType.MYSQL);
        mpg.setDataSource(dsc);
//3、包的配置
        PackageConfig pc = new PackageConfig();
        pc.setModuleName("feng");//需要将auto生成的代码放在的那一个包下面
        pc.setParent("com");
        pc.setEntity("entity");
        pc.setMapper("mapper");
        pc.setService("service");
        pc.setController("controller");
        mpg.setPackageInfo(pc);
//4、策略配置
        StrategyConfig strategy = new StrategyConfig();
        strategy.setInclude("user");//映射表名，这里也可以添加多个表
        strategy.setNaming(NamingStrategy.underline_to_camel);
        strategy.setColumnNaming(NamingStrategy.underline_to_camel);
        strategy.setEntityLombokModel(true); // 自动lombok；
        strategy.setLogicDeleteFieldName("deleted");//配置逻辑删除
// 自动填充配置
        TableFill createTime = new TableFill("create_time", FieldFill.INSERT);
        TableFill updateTime = new TableFill("update_time", FieldFill.INSERT_UPDATE);
        ArrayList<TableFill> tableFills = new ArrayList<>();
        tableFills.add(createTime);
        tableFills.add(updateTime);
        strategy.setTableFillList(tableFills);
// 乐观锁
        strategy.setVersionFieldName("version");
        strategy.setRestControllerStyle(true);
        strategy.setControllerMappingHyphenStyle(true); //   localhost:8080/hello_id_2
        mpg.setStrategy(strategy);
        mpg.execute(); //执行
    }
}

执行这个方法就会得到生成的代码了！

注意配置自己的数据库，另外，映射表名时注意对应自己表里面的字段。

    ArrayList<TableFill> tableFills = new ArrayList<>();
    tableFills.add(createTime);
    tableFills.add(updateTime);
    strategy.setTableFillList(tableFills);

// 乐观锁
strategy.setVersionFieldName(“version”);
strategy.setRestControllerStyle(true);
strategy.setControllerMappingHyphenStyle(true); // localhost:8080/hello_id_2
mpg.setStrategy(strategy);
mpg.execute(); //执行
}
}

执行这个方法就会得到生成的代码了！

注意配置自己的数据库，另外，映射表名时注意对应自己表里面的字段。