how to alter/change the post data in django UpdateView

Question

I am using django update view for my model/records editing stuff like below

class EditProductView(LoginRequiredMixin, UpdateView):
    model = Product
    def get_template_names(self):

        return ['website/product/edit_product.html']

    def get_success_url(self):

        return reverse('product_details', args=[self.kwargs['pk']])

    def get_context_data(self, **kwargs):
        publisher = Publisher.objects.get(product__id=self.kwargs['pk']) 
        context = super(EditProductView, self).get_context_data(**kwargs)
        context.update(
           {
            'publisher':publisher,
            }
          )
        return context        

edit_product =  EditProductView.as_view()   

So what all i want/trying to do is alter(add some data, edit already submitted data according to website functionality) the POST data before submitting to form,

So i know that UpdateView has some method def def post(self, request, *args, **kwargs): , but i dont know exactly how to use it

Suppose below is the request.POST data i am getting

<QueryDict: {u'product_name': [u'Biscuit'], u'product_price': [u'1000'], u'product_tag': [u'']}>

So now i want to alter the above QueryDict and if the value of product_tag was empty i need assign some default one and submit with latest querdict

Also i know that Querydict is mutable, but because of sure i need to edit the POST data, before submitting/saving to database, i need to make that querydict as dict, then edit it, and convert back to querdict

So after all whats my question is

1. How can we alter the POST data in UpdateView before submitting/saving to database
2. Is the post method heplful?

Answer 1

The QueryDict is mutable after you create its .copy(). See the docs.

Update Example:

class SomeUpdateView(UpdateView):

    def post(self, request, **kwargs):
        request.POST = request.POST.copy()
        request.POST['some_key'] = 'some_value'
        return super(SomeUpdateView, self).post(request, **kwargs)

Here is much broader discussion about the topic.

Furthermore, shouldn't this be done in ModelForm subclass? You're certainly aware you can set custom form as a form_class in UpdateView. Such a logic usually needs unit tests and it's much easier to unit test logic which sits in the form.