MybatisPlus从入门到精通

一、MyBatis-Plus核心特性

1. 无侵入性
   在MyBatis基础上增强，无需修改原有代码即可使用。
2. 自动化CRUD
   内置通用Mapper和Service，减少80%单表操作代码。
3. Lambda表达式
   支持Lambda形式的条件构造，避免字段名硬编码错误。
4. 主键策略
   支持雪花算法（ASSIGN_ID）、UUID（ASSIGN_UUID）、自增（AUTO）等主键生成方式。

二、快速入门案例

1. 数据库准备

DROP TABLE IF EXISTS sys_user;

CREATE TABLE sys_user
(
	id BIGINT NOT NULL COMMENT '主键ID',
	name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
	age INT NULL DEFAULT NULL COMMENT '年龄',
	email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
	PRIMARY KEY (id)
);
DELETE FROM sys_user;

INSERT INTO sys_user (id, name, age, email) VALUES
(1, 'Jone', 18, '[e-mail]'),
(2, 'Jack', 20, '[e-mail]'),
(3, 'Tom', 28, '[e-mail]'),
(4, 'Sandy', 21, '[e-mail]'),
(5, 'Billie', 24, '[e-mail]');

2. Spring Boot配置

pom.xml依赖：

<dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-annotation</artifactId>
            <version>3.5.3.1</version>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-core</artifactId>
            <version>3.5.3.1</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>3.0.3</version>
        </dependency>

application.yml：

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8
    username: root
    password: root

3. 实体类与Mapper

package com.awei.mybatismodel.entity;

import lombok.Data;

@Data
public class SysUser {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

package com.awei.mybatismodel.mapper;


import com.awei.mybatismodel.entity.SysUser;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;

public interface SysUserMapper extends BaseMapper<SysUser> {

}

4.启动类

package com.awei.mybatismodel;

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

@SpringBootApplication
@MapperScan("com.awei.mybatismodel.mapper")
public class MybatisModelApplication {

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

}

5.测试

package com.awei.mybatismodel;

import com.awei.mybatismodel.entity.SysUser;
import com.awei.mybatismodel.mapper.SysUserMapper;
import org.junit.jupiter.api.Assertions;
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
public class QuickStartTest {

    @Autowired
    private SysUserMapper userMapper;

    @Test
    public void testSelect() {
        System.out.println(("----- selectAll method test ------"));
        List<SysUser> userList = userMapper.selectList(null);
        Assertions.assertEquals(5, userList.size());
        userList.forEach(System.out::println);
    }
}

三、核心注解详解

注解	作用	示例
@TableName	指定实体类对应的表名	@TableName("sys_user")
@TableId	标识主键字段	@TableId(type = IdType.AUTO)
@TableField	字段与列映射/自动填充策略	@TableField(value = "email", fill = FieldFill.INSERT_UPDATE)

主键策略示例：

public enum IdType {
    AUTO,        // 数据库自增
    ASSIGN_ID,   // 雪花算法（默认）
    ASSIGN_UUID  // UUID生成
}

---

四、CRUD操作

1. 基础操作

// 插入
User user = new User();
user.setName("Tom");
userMapper.insert(user);

// 查询
User user = userMapper.selectById(1L);

// 更新
user.setAge(30);
userMapper.updateById(user);

// 删除
userMapper.deleteById(2L);

2. 条件构造器（Wrapper）

LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
wrapper.like(User::getName, "J")      // 模糊查询
       .ge(User::getAge, 18)          // 年龄>=18
       .orderByDesc(User::getCreateTime);

List<User> users = userMapper.selectList(wrapper);

生成SQL：

SELECT * FROM user WHERE name LIKE '%J%' AND age >= 18 ORDER BY create_time DESC

---

五、分页查询

1. 配置分页插件

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

2. 分页查询代码

Page<User> page = new Page<>(1, 10);  // 第1页，每页10条
LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
wrapper.eq(User::getAge, 20);

IPage<User> userPage = userMapper.selectPage(page, wrapper);
System.out.println("总记录数：" + userPage.getTotal());

---

六、高级功能

1. 逻辑删除

表字段：

ALTER TABLE user ADD is_deleted TINYINT(1) DEFAULT 0 COMMENT '逻辑删除标记';

配置：

mybatis-plus:
  global-config:
    db-config:
      logic-delete-field: isDeleted  # 逻辑删除字段名
      logic-delete-value: 1          # 删除标记值
      logic-not-delete-value: 0      # 未删除标记值

2. 自动填充

public class MetaObjectHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        this.strictInsertFill(metaObject, "createTime", LocalDateTime.class, LocalDateTime.now());
    }
}

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