P1-9：编写mapper层

新建包

新建mapper类

 

实现接口，添加注解

1 package com.dszh.demo2.mapper;
2 import com.baomidou.mybatisplus.core.mapper.BaseMapper;
3 import com.dszh.demo2.entity.User;
4 import org.springframework.stereotype.Repository;
5 
6 @Repository
7 public interface UserMapper extends BaseMapper<User> {
8 
9 }