问无法在Django中更新类模型

EN

class Class(models.Model):

    Student_List = models.ManyToManyField(User) # creates a list of different students associated with a single class 
    subject = models.ForeignKey(Subject, on_delete=models.CASCADE) # subject 
    course_ID = models.ForeignKey(CourseID, on_delete=models.CASCADE) # course ID
    callNumber = models.PositiveIntegerField(primary_key=True) # six digit number
    status = models.CharField(max_length = 50) # status open or closed
    # auto_now_add returns creation of object

    timestamp_updated = models.DateTimeField(auto_now_add=False, auto_now = True)


    def __unicode__(self):
       return str(self.callNumber) + "-----" + str(self.status) + "---------" + str(self.Student_List.all())

    # returns of all students for the class
    def get_student_list(self):
        # gets associated class_list of the Student and then gets the unicode for each class in the list
        return "\n".join([p.__unicode__() for p in self.Student_List.all()])

class ClassForm(forms.ModelForm):

class Meta:
    model = Class 
    fields = ['course_ID', 'callNumber']

def course_adder(request):

    # Raises error if user not logged in
    if not request.user.is_authenticated():
        raise Http404

    title = "Welcome to TechCheck!"


    # finds the list of courses for the current user using a filter on the queryset 
    course_list = Class.objects.filter(Student_List__email = request.user.email, Student_List__username = request.user.username)

    # forms
    form = ClassForm(request.POST or None) # create instance as a form

    if request.method == 'POST':

        if form.is_valid():
            # Never enter this part of the form because form never validates

            callNumber = form.cleaned_data.get("callNumber")
            course = Class.objects.filter(pk = callNumber)
            print course 
            print request.user 
            print course.Student_List.add(request.user)
            print course 
            print "I added a student to the class"



            callNumber = form.cleaned_data.get("callNumber")
            print callNumber, "is the call number"

            course = get_object_or_404(Class, pk=callNumber)
            Class.User.add(request.user)
            # print course
            return redirect('/user-course-status/')

        else:
            title = 'There was a problem entering your\'e data'
            context = {
            "title": title,
            "form": form,
            "course_list": course_list,
            }
            return render(request, 'html/course_adder.html', context)

    else:

        context = {
            "title": "Please enter the callNumber and correct course ID of the class you would like to get notified about.",
            "form": form,
            "course_list": course_list,
            }

        return render(request, 'html/course_adder.html', context)