Mybatis-plus快速入门与详解

作者: 背对背拥抱 | 来源:发表于2022-05-18 22:07 被阅读0次

一、MyBatis-Plus简介

1、简介

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。

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。

image-20220518205901937.png

2、特性

无侵入：只做增强不做改变，引入它不会对现有工程产生影响，如丝般顺滑
损耗小：启动即会自动注入基本 CURD，性能基本无损耗，直接面向对象操作
强大的 CRUD 操作：内置通用 Mapper、通用 Service，仅仅通过少量配置即可实现单表大部分 CRUD 操作，更有强大的条件构造器，满足各类使用需求
支持 Lambda 形式调用：通过 Lambda 表达式，方便的编写各类查询条件，无需再担心字段写错
支持主键自动生成：支持多达 4 种主键策略（内含分布式唯一 ID 生成器 - Sequence），可自由配置，完美解决主键问题
支持 ActiveRecord 模式：支持 ActiveRecord 形式调用，实体类只需继承 Model 类即可进行强大的 CRUD 操作
支持自定义全局通用操作：支持全局通用方法注入（ Write once, use anywhere ）
内置代码生成器：采用代码或者 Maven 插件可快速生成 Mapper 、 Model 、 Service 、 Controller 层代码，支持模板引擎，更有超多自定义配置等您来使用
内置分页插件：基于 MyBatis 物理分页，开发者无需关心具体操作，配置好插件之后，写分页等同于普通 List 查询
分页插件支持多种数据库：支持 MySQL、MariaDB、Oracle、DB2、H2、HSQL、SQLite、Postgre、SQLServer 等多种数据库
内置性能分析插件：可输出 SQL 语句以及其执行时间，建议开发测试时启用该功能，能快速揪出慢查询
内置全局拦截插件：提供全表 delete 、 update 操作智能分析阻断，也可自定义拦截规则，预防误操作

3、支持数据库

任何能使用 MyBatis 进行 CRUD, 并且支持标准 SQL 的数据库，具体支持情况如下，如果不在下列表查看分页部分教程 PR 您的支持。

MySQL，Oracle，DB2，H2，HSQL，SQLite，PostgreSQL，SQLServer，Phoenix，Gauss ，ClickHouse，Sybase，OceanBase，Firebird，Cubrid，Goldilocks，csiidb
达梦数据库，虚谷数据库，人大金仓数据库，南大通用(华库)数据库，南大通用数据库，神通数据库，瀚高数据库

4、框架结构

image-20220518210026312.png

5、代码及文档地址

官方地址: http://mp.baomidou.com

代码发布地址:

Github: https://github.com/baomidou/mybatis-plus
Gitee: https://gitee.com/baomidou/mybatis-plus

文档发布地址: https://baomidou.com/pages/24112f

二、入门案例

1、建表

我们使用Mysql8版本

创建表

CREATE DATABASE `mybatis_plus` /*!40100 DEFAULT CHARACTER SET utf8mb4 */;
use `mybatis_plus`;
CREATE TABLE `user` (
`id` bigint(20) NOT NULL COMMENT '主键ID',
`name` varchar(30) DEFAULT NULL COMMENT '姓名',
`age` int(11) DEFAULT NULL COMMENT '年龄',
`email` varchar(50) DEFAULT NULL COMMENT '邮箱',
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

添加数据

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、导入依赖

<dependency>
     <groupId>com.baomidou</groupId>
     <artifactId>mybatis-plus-boot-starter</artifactId>
     <version>3.5.1</version>
</dependency>
<dependency>
     <groupId>org.projectlombok</groupId>
     <artifactId>lombok</artifactId>
     <optional>true</optional>
</dependency>
<dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
     <scope>runtime</scope>
</dependency>

其中，lombok只是为了简化我们实体类的代码

IDEA 2020.3及以上版本已经内置Lombok plugin了，无需安装插件

3、application.yml

spring:
  # 配置数据源信息
  datasource:
  # 配置数据源类型
    type: com.zaxxer.hikari.HikariDataSource
    # 配置连接数据库信息
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3307/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false
    username: root
    password: root

#配置mybatis日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  # 配置MyBatis-Plus操作表的默认前缀
  global-config:
    db-config:
      table-prefix: t_
      # 配置MyBatis-Plus的主键策略
#      id-type: auto
  # 配置类型别名所对应的包
#  type-aliases-package: com.zl.po

4、启动类

在Spring Boot启动类中添加@MapperScan注解，扫描mapper包

package com.zl;

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


/**
 * @date 2022-05-15
 * @author ZL
 */
@SpringBootApplication
@MapperScan("com.zl.mapper")
public class MybatisPlusDemoApplication {

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

}

5、实体类

package com.zl.po;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableLogic;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @author zl
 * @time 2022/5/15
 */
@Data
@TableName("t_user")
public class User {

    //@TableId("uid")
    private Long id;

    //@TableField("user_name")
    private String name;

    private Integer age;

    private String email;

    /**
     * 逻辑删除
     */
    //@TableLogic
   // private Integer isDeleted;
}

6、通用Mapper接口

package com.zl.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.zl.po.User;
import org.springframework.stereotype.Repository;

/**
 * @author zl
 * @time 2022/5/15
 */
@Repository
public interface UserMapper extends BaseMapper<User> {

}

7、测试

package com.zl;

import com.zl.mapper.UserMapper;
import com.zl.po.User;
import com.zl.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.*;

/**
 * 通用Mapper测试
 */
@SpringBootTest
class MybatisPlusTest {

    @Autowired
    private UserMapper userMapper;

    /**
     * 查询所有
     * SELECT id,name,age,email FROM user
     */
    @Test
    void testSelectList() {
        List<User> users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }
}

三、进阶

1、不同数据库yml配置

Mysql

spring:
  # 配置数据源信息
  datasource:
  # 配置数据源类型
    type: com.zaxxer.hikari.HikariDataSource
    # 配置连接数据库信息
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3307/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false
    username: root
    password: root

#配置mybatis日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  # 配置MyBatis-Plus操作表的默认前缀
  global-config:
    db-config:
      table-prefix: t_
      # 配置MyBatis-Plus的主键策略
#      id-type: auto
  # 配置类型别名所对应的包
#  type-aliases-package: com.zl.po

其中mysql8的url为：

jdbc:mysql://localhost:3307/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false

mysql5的url为：

jdbc:mysql://localhost:3307/mybatis_plus?characterEncoding=utf-8&useSSL=false

Sqlserver

# DataSource Config
spring:
  datasource:
    username: sa
    password: root
    url: jdbc:sqlserver://localhost:1433;DatabaseName=test
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.microsoft.sqlserver.jdbc.SQLServerDriver

Oracle

spring:
  datasource:
    driverClassName: oracle.jdbc.OracleDriver
    username: root
    password: root
    url: jdbc:oracle:thin:@//localhost:1521/test

2、通用Service接口

Uservice

package com.zl.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.zl.po.User;

/**
 * @author zl
 * @time 2022/5/15
 */
public interface UserService extends IService<User> {
}

UserServiceImpl

package com.zl.service.impl;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.zl.mapper.UserMapper;
import com.zl.po.User;
import com.zl.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @author zl
 * @time 2022/5/15
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {
}

3、通用Mapper和通用Service常规用法

package com.zl;

import com.zl.mapper.UserMapper;
import com.zl.po.User;
import com.zl.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.*;

/**
 * 通用Mapper测试
 */
@SpringBootTest
class MybatisPlusTest {

    @Autowired
    private UserMapper userMapper;

    @Autowired
    private UserService userService;

    
    /**
     * 查询所有
     * SELECT id,name,age,email FROM user
     */
    @Test
    void testSelectList() {
        List<User> users = userMapper.selectList(null);
        users.forEach(System.out::println);
    }

    /**
     * 插入
     * INSERT INTO user ( id, name, age, email ) VALUES ( ?, ?, ?, ? )
     */
    @Test
    void testInsert(){
        User user = new User();
        user.setName("张三");
        user.setAge(23);
        user.setEmail("zhangsan@163.com");
        int result = userMapper.insert(user);
        System.out.println("受影响的行数:"+result);
        System.out.println("新建的ID："+user.getId());
    }

    /**
     * 根据ID删除
     * DELETE FROM user WHERE id=?
     */
    @Test
    void testDeleteById(){
        int result = userMapper.deleteById(1525835539440345090L);
        System.out.println("受影响的行数:"+result);
    }


    /**
     * 根据ID批量删除
     * DELETE FROM user WHERE id IN ( ? , ? )
     */
    @Test
    void testDeleteBatchIds(){
        int result = userMapper.deleteBatchIds(Arrays.asList(1L, 2L));
        System.out.println("受影响的行数:"+result);
    }


    /**
     * 根据Map删除
     * DELETE FROM user WHERE name = ? AND age = ?
     */
    @Test
    void testDeleteByMap(){
        Map<String,Object> map = new HashMap<>();
        map.put("age",21);
        map.put("name","Sandy");
        int result = userMapper.deleteByMap(map);
        System.out.println("受影响的行数:"+result);
    }


    /**
     * 根据ID更新
     * UPDATE user SET name=?, age=? WHERE id=?
     */
    @Test
    void testUpdateById(){
        User user = new User();
        user.setId(5L);
        user.setName("admin");
        user.setAge(33);

        int result = userMapper.updateById(user);
        System.out.println("受影响的行数:"+result);
    }


    /**
     * 根据ID查询
     * SELECT id,name,age,email FROM user WHERE id=?
     */
    @Test
    void testSelectById(){
        User user = userMapper.selectById(5L);
        System.out.println(user);
    }


    /**
     * 根据ID批量查询
     * SELECT id,name,age,email FROM user WHERE id IN ( ? , ? )
     */
    @Test
    void testSelectByBatchIds(){
        List<User> users = userMapper.selectBatchIds(Arrays.asList(3L, 5L));
        users.forEach(System.out::println);
    }


    /**
     * 根据Map查询
     * SELECT id,name,age,email FROM user WHERE name = ? AND age = ?
     */
    @Test
    void testSelectByMap(){
        Map<String,Object> map = new HashMap<>();
        map.put("name","admin");
        map.put("age",33);
        List<User> users = userMapper.selectByMap(map);
        users.forEach(System.out::println);
    }

    /**
     * 查询总记录数
     * SELECT COUNT( * ) FROM user
     */
    @Test
    void testGetCount(){
        long count = userService.count();
        System.out.println("总记录数:"+count);
    }


    /**
     * 批量插入：执行10次
     * INSERT INTO user ( id, name, age ) VALUES ( ?, ?, ? )
     */
    @Test
    void testSaveBatch(){
        List<User> userList = new ArrayList<>();
        for (int i=0;i<10;i++){
            User user = new User();
            user.setName("zl" + i);
            user.setAge(20 + i);
            userList.add(user);
        }

        boolean flag = userService.saveBatch(userList);
        System.out.println("插入是否成功:"+flag);
    }
}

4、Wrapper常规用法

package com.zl;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.conditions.update.LambdaUpdateWrapper;
import com.baomidou.mybatisplus.core.conditions.update.UpdateWrapper;
import com.baomidou.mybatisplus.core.toolkit.StringUtils;
import com.zl.mapper.UserMapper;
import com.zl.po.User;
import com.zl.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;
import java.util.Map;

/**
 * Wrapper测试
 * @author zl
 * @time 2022/5/15
 */
@SpringBootTest
public class MybatisPlusWrapperTest {

    @Autowired
    private UserMapper userMapper;

    @Autowired
    private UserService userService;


    /**
     * 查询用户名包含a，年龄在20到30之间，并且邮箱不为null的用户信息
     * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 AND (user_name LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)
     */
    @Test
    void test01(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like("user_name","a")
                .between("age",20,30)
                .isNotNull("email");
        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }


    /**
     * 按年龄降序查询用户，如果年龄相同则按id升序排列
     * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 ORDER BY age DESC,uid ASC
     */
    @Test
    void test02(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.orderByDesc("age").orderByAsc("uid");
        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }


    /**
     * 删除email为空的用户
     * UPDATE t_user SET is_deleted=1 WHERE is_deleted=0 AND (email IS NULL)
     */
    @Test
    void test03(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.isNull("email");
        int result = userMapper.delete(queryWrapper);
        System.out.println("影响的行数:"+result);
    }


    /**
     * 将（年龄大于20并且用户名中包含有a）或邮箱为null的用户信息修改
     * UPDATE t_user SET age=?, email=? WHERE is_deleted=0 AND (age >= ? AND user_name LIKE ? OR email IS NULL)
     */
    @Test
    void test04(){
        User user = new User();
        user.setAge(10);
        user.setEmail("zl@163.com");

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.ge("age",20)
                .like("user_name","a")
                .or()
                .isNull("email");

        int result = userMapper.update(user, queryWrapper);
        System.out.println("受影响的行数:"+result);
    }


    /**
     * 将用户名中包含有a并且（年龄大于20或邮箱为null）的用户信息修改
     * UPDATE t_user SET age=?, email=? WHERE is_deleted=0 AND (user_name LIKE ? AND (age >= ? OR email IS NULL))
     */
    @Test
    void test05(){
        User user = new User();
        user.setAge(15);
        user.setEmail("zl2@163.com");

        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like("user_name","a")
                .and(i->i.ge("age",20).or().isNull("email"));

        int result = userMapper.update(user, queryWrapper);
        System.out.println("受影响的行数："+result);
    }

    //todo 组装select子句


    /**
     * 查询用户信息的username和age字段
     * SELECT user_name,age FROM t_user WHERE is_deleted=0
     */
    @Test
    void test06(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("user_name","age");

        //selectMaps()返回Map集合列表，通常配合select()使用，避免User对象中没有被查询到的列值为null
        List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);
        maps.forEach(System.out::println);
    }


    /**
     * 将（年龄大于20或邮箱为null）并且用户名中包含有a的用户信息修改
     * UPDATE t_user SET age=?,email=? WHERE is_deleted=0 AND (user_name LIKE ? AND (age > ? OR email IS NULL))
     */
    @Test
    void test07(){
        UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
        updateWrapper.set("age",18)
                .set("email","zl@163.com")
                .like("user_name","a")
                .and(i->i.gt("age",20).or().isNull("email"));

        int result = userMapper.update(null, updateWrapper);
        System.out.println("影响行数:"+result);
    }


    /**
     * Condition条件
     * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 AND (age >= ? AND age <= ?)
     */
    @Test
    void test08(){
        //定义查询条件，有可能为null（用户未输入或未选择）
        String username = null;
        Integer ageBegin = 10;
        Integer ageEnd = 24;
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like(StringUtils.isNotBlank(username), "username", "a")
                .ge(ageBegin != null, "age", ageBegin)
                .le(ageEnd != null, "age", ageEnd);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }



    @Test
    public void test09() {
        //定义查询条件，有可能为null（用户未输入）
        String username = "a";
        Integer ageBegin = 10;
        Integer ageEnd = 24;
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        //避免使用字符串表示字段，防止运行时错误
        queryWrapper
                .like(StringUtils.isNotBlank(username), User::getName, username)
                .ge(ageBegin != null, User::getAge, ageBegin)
                .le(ageEnd != null, User::getAge, ageEnd);
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }



    @Test
    public void test10() {
        //组装set子句
        LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();
        updateWrapper
                .set(User::getAge, 18)
                .set(User::getEmail, "user@atguigu.com")
                .like(User::getName, "a")
                .and(i -> i.lt(User::getAge, 24).or().isNull(User::getEmail));
        //lambda表达式内的逻辑优先运算
        User user = new User();
        int result = userMapper.update(user, updateWrapper);
        System.out.println("受影响的行数：" + result);
    }
}

5、分页和乐观锁

1) 分页

配置类-包含分页和乐观锁

package com.zl.config;

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

/**
 * 插件配置类-包含分页插件、乐观锁
 * @author zl
 * @time 2022/5/16
 */
@Configuration
public class MybatisPlusConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        //添加分页插件
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        //添加乐观锁插件
        interceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        return interceptor;
    }
}

简单测试--查询所有

/**
     * 分页
     * SELECT uid AS id,user_name AS name,age,email,is_deleted FROM t_user WHERE is_deleted=0 LIMIT ?,?
     */
    @Test
    void testPage(){
        //当前页、每页显示条数
        Page<User> page = new Page<>(1,2);
        userMapper.selectPage(page, null);

        //获取分页数据
        List<User> list = page.getRecords();
        list.forEach(System.out::println);
        System.out.println("当前页："+page.getCurrent());
        System.out.println("每页显示的条数："+page.getSize());
        System.out.println("总记录数："+page.getTotal());
        System.out.println("总页数："+page.getPages());
        System.out.println("是否有上一页："+page.hasPrevious());
        System.out.println("是否有下一页："+page.hasNext());
    }

自定义分页接口

Mapper

/**
* 根据年龄查询用户列表，分页显示
* @param page 分页对象,xml中可以从里面进行取值,传递参数 Page 即自动分页,必须放在第一位
* @param age 年龄
* @return
*/
Page<User> selectPageVo(@Param("page") Page<User> page, @Param("age") Integer age);

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.zl.mapper.UserMapper">

    <!--  当实体类的属性名称和数据库的列名不一致时，需要用resultMap映射   -->
    <resultMap id="UserMap" type="User">
        <!-- id为主键 -->
        <id column="id" property="id"/>
        <!-- column是数据库表的列名 , property是对应实体类的属性名 -->
        <result column="uid" property="id"/>
        <result column="user_name" property="name"/>
    </resultMap>

    <!--Page<User> selectPageVo(@Param("page") Page<User> page, @Param("age") Integer age);-->
    <select id="selectPageVo" resultMap="UserMap">
        select uid,user_name,age,email from t_user where age > #{age}
    </select>

</mapper>

测试类

    /**
     *
     * 自定义分页接口
     */
    @Test
    public void testSelectPageVo(){
        //设置分页参数
        Page<User> page = new Page<>(1, 2);
        userMapper.selectPageVo(page, 10);
        //获取分页数据
        List<User> list = page.getRecords();
        list.forEach(System.out::println);
        System.out.println("当前页："+page.getCurrent());
        System.out.println("每页显示的条数："+page.getSize());
        System.out.println("总记录数："+page.getTotal());
        System.out.println("总页数："+page.getPages());
        System.out.println("是否有上一页："+page.hasPrevious());
        System.out.println("是否有下一页："+page.hasNext());
    }

2) 乐观锁

数据库表要增加一个字段version

然后用注解@Version

package com.zl.po;

import com.baomidou.mybatisplus.annotation.Version;
import lombok.Data;

/**
 * @author zl
 * @time 2022/5/16
 */
@Data
public class Product {

    private Long id;
    private String name;
    private Integer price;

    @Version
    private Integer version;
}

测试代码

/**
 * 乐观锁
 */
@Test
public void testProduct01(){
    //小李查询商品价格
    Product productLi = productMapper.selectById(1);
    System.out.println("小李查询的商品价格："+productLi.getPrice());
    //小王查询商品价格
    Product productWang = productMapper.selectById(1);
    System.out.println("小王查询的商品价格："+productWang.getPrice());
    //小李将商品价格+50
    productLi.setPrice(productLi.getPrice()+50);
    productMapper.updateById(productLi);
    //小王将商品价格-30
    productWang.setPrice(productWang.getPrice()-30);
    int result = productMapper.updateById(productWang);
    if(result == 0){
        //操作失败，重试
        Product productNew = productMapper.selectById(1);
        productNew.setPrice(productNew.getPrice()-30);
        productMapper.updateById(productNew);
    }
    //老板查询商品价格
    Product productLaoban = productMapper.selectById(1);
    System.out.println("老板查询的商品价格："+productLaoban.getPrice());
}

6、代码生成器

依赖

<!--   代码生成器  -->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-generator</artifactId>
    <version>3.5.1</version>
</dependency>
<dependency>
    <groupId>org.freemarker</groupId>
    <artifactId>freemarker</artifactId>
    <version>2.3.31</version>
</dependency>

测试类

package com.zl;

import com.baomidou.mybatisplus.generator.FastAutoGenerator;
import com.baomidou.mybatisplus.generator.config.OutputFile;
import com.baomidou.mybatisplus.generator.engine.FreemarkerTemplateEngine;
import java.util.Collections;

/**
 * @author zl
 * @time 2022/5/16
 */
public class FastAutoGeneratorTest {

    public static void main(String[] args) {
        FastAutoGenerator.create("jdbc:mysql://127.0.0.1:3307/mybatis_plus?characterEncoding=utf-8&userSSL=false", "root", "root")
                .globalConfig(builder -> {
                    builder.author("zl") // 设置作者
                            //.enableSwagger() // 开启 swagger 模式
                            .fileOverride() // 覆盖已生成文件
                            .outputDir("D://mybatis_plus"); // 指定输出目录
                })
                .packageConfig(builder -> {
                    builder.parent("com.zl") // 设置父包名
                            .moduleName("mybatisplus") // 设置父包模块名
                            .pathInfo(Collections.singletonMap(OutputFile.mapperXml, "D://mybatis_plus")); // 设置mapperXml生成路径
                })
                .strategyConfig(builder -> {
                    builder.addInclude("t_user") // 设置需要生成的表名
                            .addTablePrefix("t_", "c_"); // 设置过滤表前缀
                })
                .templateEngine(new FreemarkerTemplateEngine()) // 使用Freemarker引擎模板，默认的是Velocity引擎模板
                .execute();
    }
}

7、多数据源

依赖

<!--   多数据源  -->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
    <version>3.5.0</version>
</dependency>

配置文件

spring:
  # 配置数据源信息
  datasource:
    dynamic:
      # 设置默认的数据源或者数据源组,默认值即为master
      primary: master
      # 严格匹配数据源,默认false.true未匹配到指定数据源时抛异常,false使用默认数据源
      strict: false
      datasource:
        master:
          url: jdbc:mysql://localhost:3307/mybatis_plus?characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true
          driver-class-name: com.mysql.cj.jdbc.Driver
          username: root
          password: root
        slave_1:
          url: jdbc:mysql://localhost:3307/mybatis_plus_1?characterEncoding=utf-8&useSSL=false
          driver-class-name: com.mysql.cj.jdbc.Driver
          username: root
          password: root
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  type-aliases-package: com.zl.po

在UserServiceImpl上加上注解@DS

package com.zl.service.impl;

import com.baomidou.dynamic.datasource.annotation.DS;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.zl.mapper.UserMapper;
import com.zl.po.User;
import com.zl.service.UserService;
import org.springframework.stereotype.Service;

/**
 * @author zl
 * @time 2022/5/15
 */
//指定所操作的数据源
@DS("master") 
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService {
}

8、MybatisX插件

MyBatis-Plus为我们提供了强大的mapper和service模板，能够大大的提高开发效率

但是在真正开发过程中，MyBatis-Plus并不能为我们解决所有问题，例如一些复杂的SQL，多表联查，我们就需要自己去编写代码和SQL语句，我们该如何快速的解决这个问题呢，这个时候可以使用MyBatisX插件 MyBatisX一款基于 IDEA 的快速开发插件，为效率而生。

MyBatisX插件用法：https://baomidou.com/pages/ba5b24