Форма Django недействительна

Этот вопрос может быть задан много раз в stackoverflow, но я не смог найти ответ. Взгляните на код:

# models.py
class Message(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    body = models.CharField(max_length=200, null=True, blank=True)
    room = models.ForeignKey(Room, on_delete=models.CASCADE, blank=True, null=True)
    posted = models.TimeField(auto_now_add=True)

    def __str__(self):
        return self.body

views.py:

class RoomInsideView(View):
    template_name = 'room/room_inside.html'
    form_class = SendMessageForm
    room = None

    def get(self, request, room_id, room_slug):
        self.room = Room.objects.get(id=room_id)
        if self.room.is_private:
            return redirect('room:private_room_auth', self.room.id)
        form = self.form_class()
        context =  {
                    'room': self.room,
                    'form': form,
        }
        return render(request, self.template_name, context)

    def post(self, request, room_id, room_slug):
        form = self.form_class(request.POST)
        if form.is_valid():
           new_msg = Message(body=form.cleaned_data['body'])
           new_msg.user = request.user  in
           all_messages = Message.objects.filter(room=self.room)
        messages.error(request, 'form not valid', 'warning')
        return render(request, self.template_name, {'form': form, 'message': all_messages})

forms.py:

class SendMessageForm(forms.ModelForm):
    class Meta:
        model = Message
        fields = ('body',)
        widgets = {
            'body': forms.TextInput(attrs={'class': 'form-control',
                                           'placeholder': 'Send'}),
        }

Шаблон:

    <form method="post" action="" novalidate>
        {% csrf_token %}
        {{ form.non_field_errors }}
        {{ form.body.errors }}
        {{ form.body }}
        <input type="submit" value="Send" class="btn btn-primary">
    </form>

Так как я добавил messages.error если форма не действительна она возвращает форму не действительной и я не могу найти где я делаю неправильно

class RoomInsideView(View):
    template_name = 'room/room_inside.html'
    form_class = SendMessageForm
    success_url = reverse_lazy('name-of-some-view')

    def get_context_data(self, *args, **kwargs):
        context = super().get_context_data(*args, **kwargs)
        context['room'] = get_object_or_404(Room, pk=self.kwargs['room_id'], is_private=False)
        return context

    def form_invalid(self, form):
        messages.error(request, 'form not valid', 'warning')
        return super().form_invalid(form)

    def form_valid(self, form):
        form.instance.room_id = self.kwargs['room_id']
        form.instance.user = self.request.user
        return super().form_valid(form)