mybatis-plus快速入门

mybatis-plus是什么

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

快速入门

开发环境
IDE：idea 2019.2
JDK：JDK8
构建工具：maven 3.x
MySQL版本：MySQL 8.0.27
Spring Boot：2.5.8
MyBatis-Plus：3.5.1

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, '[email protected]' ),
	( 2, 'Jack', 20, '[email protected]' ),
	( 3, 'Tom', 28, '[email protected]' ),
	( 4, 'Sandy', 21, '[email protected]' ),
	( 5, 'Billie', 24, '[email protected]' );

引入依赖
新建spring boot项目并引入依赖

        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
        dependency>
        
        <dependency>
            <groupId>org.projectlombokgroupId>
            <artifactId>lombokartifactId>
            <version>1.18.10version>
            <scope>providedscope>
        dependency>
        
        <dependency>
            <groupId>com.baomidougroupId>
            <artifactId>mybatis-plus-boot-starterartifactId>
            <version>3.5.1version>
        dependency>

yml文件

spring:
  datasource:
    username: root
    password: 123456
    #?serverTimezone=UTC解决时区的报错
    url: jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8
    driver-class-name: com.mysql.cj.jdbc.Driver
    type: com.zaxxer.hikari.HikariDataSource

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

添加实体

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("user")
public class User {
    @TableId(value = "id")
    private Long id;

    @TableField(value = "name")
    private String name;
    private Integer age;
    private String email;
}

mapper类

@Mapper
public interface UserService extends IService<User> {
    
}

UserService类

public interface UserService extends IService<User> {
    
}

UserServiceImpl类

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

controller类

@RequestMapping("/mybatisplus")
@Controller
public class MybatisPlusController {
    @Autowired
    private UserMapper userMapper;
    @Autowired
    private UserService userService;
	
	//...
}

使用
mybatis-plus的CRUD实在过于简单，根据名字都能猜个大概，这里不展开说了，这里只举两个简单的例子

    @RequestMapping("/deleteByMap")
    @ResponseBody
    public String deleteByMap(){
        HashMap<String, Object> map = new HashMap<>();
        map.put("age", 23);
        map.put("name","张三");

        //相当于//DELETE FROM user WHERE name = ? AND age = ?
        int i = userMapper.deleteByMap(map);
        return String.valueOf(i);
    }

    @RequestMapping("/updateById")
    @ResponseBody
    public String updateById(){
        User user = new User(5L, "admin", 22, null);
        //UPDATE user SET name=?, age=? WHERE id=?
        int result = userMapper.updateById(user);
        return String.valueOf(result);
    }

条件构造器和常用接口

Wrapper ： 条件构造抽象类，最顶端父类
-AbstractWrapper ： 用于查询条件封装，生成 sql 的 where 条件
QueryWrapper ： 查询条件封装
UpdateWrapper ： Update 条件封装
AbstractLambdaWrapper ： 使用Lambda 语法
LambdaQueryWrapper ：用于Lambda语法使用的查询Wrapper
LambdaUpdateWrapper ： Lambda 更新封装Wrapper

QueryWrapper的使用

    @RequestMapping("/queryWrapper1")
    @ResponseBody
    public String queryWrapper1(){
        //相当于SELECT id,name,age,email FROM user WHERE (name LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like("name", "a");
        wrapper.between("age", 20, 30);
        wrapper.isNotNull("email");

        List<User> list = userMapper.selectList(wrapper);
        return JSON.toJSONString(list);
    }

分页插件

配置类

@Configuration
public class MybatisPlusConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

测试类

    @RequestMapping("/testPage")
    @ResponseBody
    public String testPage(){
        Page<User> page = new Page<>(1,3);

        userMapper.selectPage(page, null);
        return JSON.toJSONString(page);
    }