1 简介

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。MyBatis-Plus提供了通用的mapper和service，可以在不编写任何SQL语句的情况下，快速的实现对单表的CRUD、批量、逻辑删除、分页等操作。

2 初始化项目

2.1引入pom

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

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

        <!-- mybatis-plus -->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>
        <!-- 简化实体类开发 -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <!-- mysql驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>

2.2 引入lombok插件

2.3 配置信息

spring:
# 配置数据源信息
  datasource:
# 配置数据源类型（spring默认的数据源）
    type: com.zaxxer.hikari.HikariDataSource
# 配置连接数据库信息（配置驱动类，版本为8）
    driver-class-name: com.mysql.cj.jdbc.Driver
#mysql8版本的写法
    url: jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false
    username: root
    password: yuan159951.

# mysql5版本的写法
# driver-class-name: com.mysql.jdbc.Driver
# url: jdbc:mysql://localhost:3306/mybatis_plus?characterEncoding=utf-8&useSSL=false

2.4 创建实体类

import lombok.Data;

@Data //lombok注解
public class User {
        private Long id;
        private String name;
        private Integer age;
        private String email;   
}

2.5 创建mapper

import com.yunfeng.mybatisplus.pojo.User;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;

public interface UserMapper extends BaseMapper<User> {
}

2.6 配置注解MapperScan

@SpringBootApplication
//扫描mapper接口所在的包
@MapperScan("com.yunfeng.mybatisplus.mapper")
public class MybatisplusApplication {

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

}

2.7 编写测试类

import com.yunfeng.mybatisplus.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
public class MybatisPlusTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectList(){
        //selectList()根据MP内置的条件构造器查询一个list集合，null表示没有条件，即查询所有
        userMapper.selectList(null).forEach(System.out::println);
    }
}

2.8 配置MyBatis日志

# 配置MyBatis日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

3 测试基本的CRUD

3.1 新增

@Test
    public void testInsert(){
        User user = new User();
        user.setName("张三");
        user.setAge(18);
        user.setEmail("302976975@qq.com");
        int row = userMapper.insert(user);
        System.out.println("row = " + row);
        System.out.println(user.getId());
    }

3.2 查询

    @Test
    public void testSelectById(){
//        User user = userMapper.selectById(1L);
//        System.out.println(user);
//        List<Long> longs = Arrays.asList(1l, 2l, 3l);
//        List<User> users = userMapper.selectBatchIds(longs);
//        System.out.println("users = " + users);
//        Map<String,Object> map = new HashMap<>();
//        map.put("name","jack");
//        map.put("age",20);
//        List<User> users = userMapper.selectByMap(map);
//        System.out.println("users = " + users);
        List<User> users = userMapper.selectList(null);
        System.out.println("users = " + users);
    }

3.3 修改

@Test
    public void testUpdateById(){
        User user = new User();
        user.setId(4L);
        user.setName("李四");
        int result = userMapper.updateById(user);
        System.out.println("受影响行数："+result);
    }

3.4 删除

    @Test
    public void testDeleteById(){
//        int result = userMapper.deleteById(1595594324846141442L);
//        System.out.println("受影响行数："+result);
//        Map<String,Object> map = new HashMap<>();
//        map.put("name","张三");
//        map.put("age",18);
//        userMapper.deleteByMap(map);
        List<Long> longs = Arrays.asList(1l, 2l, 3l);
        int rows = userMapper.deleteBatchIds(longs);
        System.out.println("rows = " + rows);
    }

4 自定义动态sql

• 默认位置可以不写！
  
• 新增mybatis模板文件
  
• 官方模板文件

<?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.yunfeng.mybatisplus.mapper.UserMapper">

</mapper>

• UserMapper接口代码

Map<String,Object> selectMapById(Long id);

• UserMapper.xml代码

<select id="selectMapById" resultType="map">
        select * from user where id = #{id}
    </select>

• 测试类

Map<String, Object> map = userMapper.selectMapById(1l);
        System.out.println("map = " + map);

5 Service 层使用mybatis-plus方法

5.1 service层代码

• 接口

public interface UserService  extends IService<User> {
}

• 实现类

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper,User> implements UserService{

}

5.2 测试查询总记录数

@Test
    public void testGetCount(){
        long count = userService.count();
        System.out.println("count = " + count);
    }

5.3 测试批量新增

	@Test
    public void testSaveBatch(){
// SQL长度有限制，海量数据插入单条SQL无法实行，
// 因此MP将批量插入放在了通用Service中实现，而不是通用Mapper
        ArrayList<User> users = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            User user = new User();
            user.setName("ybc" + i);
            user.setAge(20 + i);
            users.add(user);
        }
//SQL:INSERT INTO t_user ( username, age ) VALUES ( ?, ? )
        boolean bool = userService.saveBatch(users);
        System.out.println("bool = " + bool);
    }

6 id不是用雪花算法，自己定义

@Data //lombok注解
@TableName("user")
public class User {

//IdType.AUTO就是自增
        @TableId(value = "id",type = IdType.AUTO)
        private Long id;
        @TableField("name")
        private String name;
        private Integer age;
        private String email;
		//逻辑删除
        @TableLogic
        private Integer isDeleted;
}

• 配置方法

# 配置MyBatis
mybatis-plus:
  configuration:
    # 日志信息
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    db-config:
      # 配置MyBatis-Plus的主键策略
      id-type: auto
    # 配置MyBatis-Plus操作表的默认前缀
#      table-prefix:
  # 配置类型别名所对应的包
  type-aliases-package: com.yunfeng.mybatisplus.pojo
  # 配置扫描通用枚举
  type-enums-package: com.yunfeng.mybatisplus.enums

7 雪花算法

雪花算法是由Twitter公布的分布式主键生成算法，它能够保证不同表的主键的不重复性，以及相同表的
主键的有序性。

• 和时间有关。
• ①核心思想：
  长度共64bit（一个long型）。
  首先是一个符号位，1bit标识，由于long基本类型在Java中是带符号的，最高位是符号位，正数是0，负
  数是1，所以id一般是正数，最高位是0。
  41bit时间截(毫秒级)，存储的是时间截的差值（当前时间截 - 开始时间截)，结果约等于69.73年。
  10bit作为机器的ID（5个bit是数据中心，5个bit的机器ID，可以部署在1024个节点）。
  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）。
• ②优点：整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞，并且效率较高。
  

8 wapper条件构造器

8.1 QueryWrapper（查询、删除、修改）

• 查询

	@Test
    public void test01(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like("name","a")
                .between("age",20,30)
                .isNotNull("email");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

• 查询排序

	@Test
    public void test02(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.orderByDesc("age")
                .orderByAsc("id");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

• 删除

	@Test
    public void test03(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.isNull("email");
        int row = userMapper.delete(queryWrapper);
        System.out.println("row = " + row);
    }

• 条件修改

	@Test
    public void test04(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.gt("age",20)
                .like("name","a")
                .or()
                .isNull("email");
        User user = new User();
        user.setName("张三");
        int rows = userMapper.update(user, queryWrapper);
        System.out.println("rows = " + rows);
    }

• lambda中的条件优先执行

@Test
    public void test05(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        //lambda中的条件优先执行
        queryWrapper.like("name","a")
                .and(i -> i.gt("age",20).or().isNull("email"));
        User user = new User();
        user.setName("李四");
        int rows = userMapper.update(user, queryWrapper);
        System.out.println("rows = " + rows);
    }

• 查询部分字段

//查询部分字段
    @Test
    public void test06(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.select("name","age");
        List<Map<String, Object>> maps = userMapper.selectMaps(queryWrapper);
        maps.forEach(System.out::println);
    }

• 子查询

// 子查询
    @Test
    public void test07(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.inSql("age","select age from user where age < 20");
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

8.2 UpdateWrapper

• UpdateWrapper修改不需要new实体类

@Test
    public void test08(){
        UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
        updateWrapper.like("name","a")
                .and( i -> i.gt("age",20).or().isNull("email"));
        updateWrapper.set("name","王五");
        int rows = userMapper.update(null, updateWrapper);
        System.out.println("rows = " + rows);
    }

• 条件组装

@Test
    public void test10(){
        String name = "";
        Integer ageBegin = 20;
        Integer ageEnd = 30;
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.like(StringUtils.isNotBlank(name),"name",name)
                .ge(ageBegin != null,"age",ageBegin)
                .gt(ageEnd != null,"age",ageEnd);
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

8.3 LambdaQueryWrapper

@Test
    public void test11(){
        String name = "";
        Integer ageBegin = 20;
        Integer ageEnd = 30;
        LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.like(StringUtils.isNotBlank(name),User::getName,name)
                .ge(ageBegin != null,User::getAge,ageBegin)
                .gt(ageEnd != null,User::getAge,ageEnd);
        List<User> users = userMapper.selectList(queryWrapper);
        users.forEach(System.out::println);
    }

8.4 LambdaUpdateWrapper

@Test
    public void test12(){
        LambdaUpdateWrapper<User> updateWrapper = new LambdaUpdateWrapper<>();
        updateWrapper.like(User::getName,"a")
                .and( i -> i.gt(User::getAge,20).or().isNull(User::getEmail));
        updateWrapper.set(User::getName,"赵六");
        int rows = userMapper.update(null, updateWrapper);
        System.out.println("rows = " + rows);
    }

9 插件

9.1 分页插件

• 写配置类

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

@Configuration
//扫描mapper接口所在的包
@MapperScan("com.atguigu.mybatisplus.mapper")
public class MyBatisPlusConfig {

    //分页插件
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }

}

• 测试

@Test
    public void testPage(){
        Page<User> page = new Page<>(2,3);
        userMapper.selectPage(page, null);
        System.out.println("page = " + page);
    }

9.2 乐观锁和悲观锁

• 添加@Version注解

@Data
public class Product {
private Long id;
private String name;
private Integer price;
@Version
private Integer version;
}

• 添加插件

@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;
}

10 代码生成器

• 官网地址：https://baomidou.com/pages/779a6e/#%E5%AE%89%E8%A3%85

10.1引入以依赖

<!-- 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>

10.2 生成代码

public static void main(String[] args) {
        FastAutoGenerator.create("jdbc:mysql://127.0.0.1:3306/mybatis_plus?characterEncoding=utf-8&userSSL=false", "root", "yuan159951.")
                .globalConfig(builder -> {
                    builder.author("logic") // 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.yunfeng") // 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("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();
    }