使用Mybatis-plus需要使用两个依赖包（缺一不可）

       <!-- 导入mybatis-plus--><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus</artifactId><version>3.4.2</version></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>3.1.0</version></dependency>

dao层需要继承BaseMapper

@Repository
public interface GradeDao extends BaseMapper<Grade> {}

ctroller层代码
增删改改查

// 查所有
List<Grade> grades = gradeDao.selectList(null);

int i = gradeDao.insert(grade);//增
int i = gradeDao.deleteById(id);//删
int i = gradeDao.updateById(grade);//改
Grade grade = gradeDao.selectById(id);//单查

附带条件的查询
具体条件文档可以在
条件选择器里面找到

        QueryWrapper wrapper = new QueryWrapper();wrapper.eq("chinese", a);List<Grade> list = gradeDao.selectList(wrapper);

分页查询
首先手写MyBatisPlusConfig配置

	@Beanpublic PaginationInterceptor paginationInnerInterceptor(){return new PaginationInterceptor();}

        Page<Grade> page = new Page<>(1,2);Page<Grade> grades = gradeDao.selectPage(page,null);