mybatis-plus快速入门，手把手搭建mybatis-plus第一个项目

请查看官网开发文档：mybatis-plus官网

 

步骤

1. 创建数据库及user表

CREATE DATABASE /*!32312 IF NOT EXISTS*/ `mybatisdemo` /*!40100 DEFAULT CHARACTER SET utf8mb4 */;
USE mybatisdemo;
DROP TABLE IF EXISTS USER;
CREATE TABLE USER
(
    id BIGINT(20) NOT NULL COMMENT '主键ID',
    NAME VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
    age INT(11) NULL DEFAULT NULL COMMENT '年龄',
    email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
    PRIMARY KEY (id)
);
DELETE FROM USER;
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]');

2. 编写项目，创建springboot项目，初始化项目！

3. 导入依赖

        
		
			mysql
			mysql-connector-java
		

		
		
			org.projectlombok
			lombok
			1.18.20
		

		
		
			com.baomidou
			mybatis-plus-boot-starter
			3.5.1
		

说明：使用mybatis-plus可以节省大量的代码，尽量不要同时导入mybatis和mybatis-plus

4. 连接数据库，与mybatis相同

spring.datasource.driverClassName: com.mysql.cj.jdbc.Driver
spring.datasource.url: jdbc:mysql://127.0.0.1:3306/mybatisdemo?useUnicode=true&characterEncoding=utf-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=GMT%2B8
spring.datasource.username: root
spring.datasource.password: 123456

5.pojo-dao (连接mybatis，配mapper.xml文件） -service-controller（传统方式）

5.使用mybatis-plus后

pojo:

 

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

mapper接口:

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.mybatis.mybatisdemo.pojo.User;
import org.springframework.stereotype.Repository;

// 在对应的mapper上面实现基本接口BaseMapper
@Repository  //代表持久层
public interface UserMapper  extends BaseMapper {
    //所有的CRUD已经编写完成
    //不需要写一大堆配置文件
}

 

 

 

以下是baseMapper底层代码，T即为传输进来的类

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.baomidou.mybatisplus.core.mapper;

import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;
import com.baomidou.mybatisplus.core.toolkit.ExceptionUtils;
import java.io.Serializable;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.annotations.Param;

public interface BaseMapper extends Mapper {
    int insert(T var1);

    int deleteById(Serializable var1);

    int deleteById(T var1);

    int deleteByMap(@Param("cm") Map var1);

    int delete(@Param("ew") Wrapper var1);

    int deleteBatchIds(@Param("coll") Collection var1);

    int updateById(@Param("et") T var1);

    int update(@Param("et") T var1, @Param("ew") Wrapper var2);

    T selectById(Serializable var1);

    List selectBatchIds(@Param("coll") Collection var1);

    List selectByMap(@Param("cm") Map var1);

    default T selectOne(@Param("ew") Wrapper queryWrapper) {
        List ts = this.selectList(queryWrapper);
        if (CollectionUtils.isNotEmpty(ts)) {
            if (ts.size() != 1) {
                throw ExceptionUtils.mpe("One record is expected, but the query result is multiple records", new Object[0]);
            } else {
                return ts.get(0);
            }
        } else {
            return null;
        }
    }

    default boolean exists(Wrapper queryWrapper) {
        Long count = this.selectCount(queryWrapper);
        return null != count && count > 0L;
    }

    Long selectCount(@Param("ew") Wrapper var1);

    List selectList(@Param("ew") Wrapper var1);

    List> selectMaps(@Param("ew") Wrapper var1);

    List