**Service:** ``` public interface ChooseCourseService extends IMppService<ChooseCourse> { } ``` ``` @Service public class ChooseCourseServiceImpl extends MppServiceImpl<ChooseCourseMapper, ChooseCourse> implements ChooseCourseService { } ``` **Mapper** ``` public interface ChooseCourseMapper extends MppBaseMapper<ChooseCourse> { int insertChosenCourse(Integer userId, Integer courseId); int deleteChosenCourse(Integer userId, Integer courseId); ChooseCourse selectChooseCourseByUserIdAndCourseId(Integer userId,Integer courseId); } ``` jdk 19 mpp-1.7.4