Модель Formset показывает ошибку при обновлении моей формы

Question

Форма создается идеально, но когда я пытаюсь обновить форму, набор форм модели не обновляется, так как показывает данные, но когда я изменяю данные и отправляю их, fliefield lecture_content показывает пустой. Я теряю заполненное файловое поле при отправке формы .def content_edit_view (request, id): course = get_object_or_404 (Course, id = id) LectureFormset = modelformset_factory (Lecture, fields = ('lecture_title', 'lecture_content'), extra = 0)

if course.user != request.user:
    raise Http404()

if request.method == 'POST':
    content_edit_form = ContentEditForm(request.POST or None, request.FILES or None, instance=course)
    formset = LectureFormset(request.POST or None, request.FILES or None)

    if content_edit_form.is_valid() and formset.is_valid():
        content_edit_form.save()
        print('course is saved')

        data = Lecture.objects.filter(post=post)

        # give index of the item for a formset item strting form 0 and (f)the item itself 
        for index, f in enumerate(formset):
            if f.cleaned_data:
                if f.cleaned_data['id'] is None:
                    video = Lecture(course=course, lecture_title=f.cleaned_data.get('lecture_title'), lecture_content=f.cleaned_data.get('lecture_content'))
                    video.save()
                else:
                    video = Lecture(course=course, lecture_title=f.cleaned_data.get('lecture_title'), lecture_content=f.cleaned_data.get('lecture_content'))              
                    d = Lecture.objects.get(id=data[index].id) #get slide id which was uploaded
                    d.lecture_title = video.lecture_title, # changing the database tiitle with new title
                    d.lecture_content = video.lecture_content # changing the database content with new content
                    d.save()

        return redirect('teacher-profile')

    else:
        print("form invalid")

else:
    content_edit_form = ContentAddForm(instance=course)
    formset = LectureFormset(queryset=Lecture.objects.filter(course=course))

context = {
    'contentForm': content_edit_form,
    'course': course,
    'formset': formset,
}


return render(request, 'apps/contentAdd.html', context)

`