public async Task <long> InsertCourseByUserIdAsync(long userId, Course course) { if (userId < 0) { throw new ArgumentException(); } //根据userId找出teacher var teacher = await _iUserService.GetUserByUserIdAsync(userId); //会抛出ArgumentException和UserNotFoundException course.Teacher = teacher; var courseId = await _iCourseDao.InsertCourseByUserIdAsync(course); return(courseId); }