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。本文主要介绍 Mybatis-Plus 的基本使用，相关的环境及软件信息如下：Spring Boot 2.6.12、Mybatis-Plus 3.5.2。

1、Mybatis-Plus 简介

1.1、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

1.2、支持数据库

• 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

1.3、框架结构

2、Mybatis-Plus 使用

这里演示下 Mybatis-plus 的基本使用，工程目录结构如下：

2.1、pom.xml

主要配置如下：

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>com.baomidou</groupId>
        <artifactId>mybatis-plus-boot-starter</artifactId>
        <version>3.5.2</version>
    </dependency>

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

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

    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.24</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
        <scope>test</scope>
    </dependency>
</dependencies>
<build>
    <resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.xml</include>
            </includes>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
        </resource>
    </resources>
</build>

2.2、配置

2.2.1、应用配置(application.yml)

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://10.49.196.23:3306/test?useUnicode=true&characterEncoding=UTF-8
    username: root
    password: 123456

mybatis-plus:
  configuration:
    map-underscore-to-camel-case: true
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

2.2.2、日志配置(logback.xml)

<?xml version="1.0" encoding="utf-8"?>
<configuration debug="false">
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
          <level>INFO</level>
        </filter>
        
        <encoder>
            <pattern>%d %-5level [%thread] %logger[%L] -> %m%n</pattern>
        </encoder>
    </appender>

    <root level="info">
        <appender-ref ref="STDOUT" />
    </root>

    <logger name="com.abc.mapper" level="debug">
    </logger>
    <logger name="com.baomidou.mybatisplus" level="debug">
    </logger>
</configuration>

2.3、创建 Mybatis-Plus 配置类

package com.abc.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 MybatisConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        //分页插件
        PaginationInnerInterceptor pageInterceptor = new PaginationInnerInterceptor();
        //设置请求的页面大于最大页后操作，true调回到首页，false继续请求。默认false
        pageInterceptor.setOverflow(false);
        //单页分页条数限制，默认无限制
        pageInterceptor.setMaxLimit(500L);
        //设置数据库类型
        pageInterceptor.setDbType(DbType.MYSQL);
        interceptor.addInnerInterceptor(pageInterceptor);
        return interceptor;
    }
}

2.4、创建实体类

package com.abc.entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;
import lombok.ToString;

import java.time.LocalDateTime;

@ToString
@Data
@TableName("a_student")
public class Student {
    @TableId(type = IdType.AUTO)
    private Long id;

    private LocalDateTime createTime;

    private LocalDateTime modifyTime;

    private String name;

    private Integer age;

    private String homeAddress;
}

表 a_student 的字段与实体类的属性一一对应(表中字段使用下划线写法，实体类属性使用驼峰写法)，字段 id 为自增字段。

2.5、创建 Mapper

package com.abc.mapper;

import com.abc.entity.Student;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;

import java.util.List;
import java.util.Map;

@Mapper
public interface StudentMapper extends BaseMapper<Student> {
    List<Student> select(@Param("name") String name, @Param("homeAddress") String homeAddress);

    List<Map<String, Object>> select2(String name, String homeAddress);
}

Mybatis-Plus 的 BaseMapper 提供了基础的增删改查功能，如果不能满足需求，可以再定义额外的方法，对应的 XML 文件(StudentMapper.xml)内容为：

<?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.abc.mapper.StudentMapper">
    <select id="select" resultType="com.abc.entity.Student">
        select * from a_student where 1=1
        <if test="name != null and name != ''">
            and name like #{name}
        </if>
        <if test="homeAddress != null and homeAddress != ''">
            and home_address like #{homeAddress}
        </if>
    </select>

    <select id="select2" resultType="map">
        select * from a_student where 1=1
        <if test="param1 != null and param1 != ''">
            and name like #{param1}
        </if>
        <if test="param2 != null and param2 != ''">
            and home_address like #{param2}
        </if>
    </select>
</mapper>

2.6、创建 Service

package com.abc.service;


import com.abc.entity.Student;
import com.abc.mapper.StudentMapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Map;

@Service
public class StudentService extends ServiceImpl<StudentMapper, Student> {
    public List<Student> select(String name, String homeAddress) {
        return baseMapper.select(name, homeAddress);
    }

    public List<Map<String, Object>> select2(String name, String homeAddress) {
        return baseMapper.select2(name, homeAddress);
    }
}

Mybatis-Plus 的 ServiceImpl 进一步封装了增删改查的功能，可以更好的满足业务需求；当然对于特定的业务需求也可以定义自己的方法。

2.7、测试用例

2.7.1、Mapper 测试用例

package com.abc.mapper;

import com.abc.entity.Student;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentMapperCase {
    private static final Logger logger = LoggerFactory.getLogger(StudentMapperCase.class);

    @Autowired
    private StudentMapper studentMapper;

    @Test
    public void insert() {
        Student student = new Student();
        student.setCreateTime(LocalDateTime.now());
        student.setName("李白");
        student.setAge(30);
        student.setHomeAddress("长安");
        studentMapper.insert(student);
        logger.info("id={}", student.getId());
    }

    @Test
    public void update() {
        Student student = new Student();
        student.setId(261L);
        student.setName("李白2");
        studentMapper.updateById(student);
    }

    @Test
    public void selectById() {
        Student student = studentMapper.selectById(261L);
        logger.info(student.toString());
    }

    @Test
    public void select() {
        List<Student> students = studentMapper.select("%李%", "%长%");
        logger.info(students.toString());
    }

    @Test
    public void selectForPage() {
        Page<Student> page = new Page<>(1, 3);
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.like("name", "%李%");
        queryWrapper.like("home_address", "%长%");
        Page<Student> result = studentMapper.selectPage(page, queryWrapper);
        logger.info(result.getRecords().toString());
    }

    @Test
    public void select2() {
        List<Map<String, Object>> list = studentMapper.select2("%李%", "%长%");
        logger.info(list.toString());
    }

    @Test
    public void delete() {
        List<Long> list = new ArrayList(){{
            add(260L);
            add(263L);
        }};
        studentMapper.deleteBatchIds(list);
    }
}

2.7.2、Service 测试用例

package com.abc.service;

import com.abc.entity.Student;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

@RunWith(SpringRunner.class)
@SpringBootTest
public class StudentServiceCase {
    private static final Logger logger = LoggerFactory.getLogger(StudentServiceCase.class);

    @Autowired
    private StudentService studentService;

    @Test
    public void insert() {
        Student student = new Student();
        student.setCreateTime(LocalDateTime.now());
        student.setName("李白");
        student.setAge(30);
        student.setHomeAddress("长安");
        studentService.save(student);
        logger.info("id={}", student.getId());
    }

    @Test
    public void update() {
        Student student = new Student();
        student.setId(261L);
        student.setName("杜甫");
        studentService.saveOrUpdate(student);
    }

    @Test
    public void selectById() {
        Student student = studentService.getById(261L);
        logger.info(student.toString());
    }

    @Test
    public void select() {
        List<Student> students = studentService.select("%李%", "%长%");
        logger.info(students.toString());
    }

    @Test
    public void selectForPage() {
        Page<Student> page = new Page<>(1, 3);
        QueryWrapper queryWrapper = new QueryWrapper();
        queryWrapper.like("name", "%李%");
        queryWrapper.like("home_address", "%长%");
        Page<Student> result = studentService.page(page, queryWrapper);
        logger.info(result.getRecords().toString());
    }

    @Test
    public void select2() {
        List<Map<String, Object>> list = studentService.select2("%李%", "%长%");
        logger.info(list.toString());
    }

    @Test
    public void delete() {
        List<Long> list = new ArrayList(){{
            add(260L);
            add(263L);
        }};
        studentService.removeBatchByIds(list);
    }
}

 

更多详细说明及使用方法请参考官网文档：https://baomidou.com/。