Updating context data in FormView form_valid method?

Question

I have a class QuestionView which is derived from the FormView class. Here is a code snippet to explain my problem:

class QuestionView(FormView):
    ...
    context_var1 = y

    def form_valid (self, form):
        ...
        self.context_var1 = x
        ...

    def get_context_data(self, **kwargs):
        ...
        context['context_var1'] = self.context_var1
        ...
        return context

As shown above, I update a set of context variables in form_valid and I intend to use the updated values of these in the template - hence the variables in the context dictionary. The problem with this code is that the change in context_var1 isn't seen - might be because get_context_data is called before the form_valid method. Is there is a workaround for this?

Answer 1

I do this with form_invalid. Here's how I do it:

from django.views.generic import FormView

class ContextFormView(FormView):
    def get(self, request, *args, **kwargs):
        form_class = self.get_form_class()
        form = self.get_form(form_class)
        context = self.get_context_data(**kwargs)
        context['form'] = form
        return self.render_to_response(context)

    def post(self, request, *args, **kwargs):
        form_class = self.get_form_class()
        form = self.get_form(form_class)
        if form.is_valid():
            return self.form_valid(form)
        else:
            return self.form_invalid(form, **kwargs)

    def form_invalid(self, form, **kwargs):
        context = self.get_context_data(**kwargs)
        context['form'] = form
        return self.render_to_response(context)

You could do the same but for form_valid. Normally the body of form_valid looks like this:

def form_valid(self, form):
    return HttpResponseRedirect(self.get_success_url())

You would have to override both post and form_valid, because post calls form_valid.

def post(self, request, *args, **kwargs):
    form_class = self.get_form_class()
    form = self.get_form(form_class)
    if form.is_valid():
        return self.form_valid(form, **kwargs)
    else:
        return self.form_invalid(form, **kwargs)

def form_valid(self, form, **kwargs):
    # take some other action here
    return HttpResponseRedirect(self.get_success_url())

oh and just to clarify, the reason this problem exists is that the ProcessFormView class's get method is broken. It normally looks like this:

def get(self, request, *args, **kwargs):
    form_class = self.get_form_class()
    form = self.get_form(form_class)
    return self.render_to_response(self.get_context_data(form=form))

It just throws the kwargs away (._.)

Answer 2

In Django 2.0.1 you can insert context data by overriding either get_context_data or form_invalid.

In your case you could do one of the following overrides:

class QuestionView(FormView):
    ...

    def form_invalid(self, form):
        """If the form is invalid, render the invalid form."""
        return self.render_to_response(
            self.get_context_data(
                form=form, 
                context_key=some_value
            )
        )

Or:

class QuestionView(FormView):
    ...

    def get_context_data(self, **kwargs):
        if 'context_key' not in kwargs:  # set value if not present
            kwargs['context_key'] = some_value
        return super().get_context_data(**kwargs)

Django 2.0.1 inserts under the hood the form into the kwargs of get_context_data.

# File: django.views.generic.edit

class FormMixin(ContextMixin):
    ...

    def form_valid(self, form):
        """If the form is valid, redirect to the supplied URL."""
        return HttpResponseRedirect(self.get_success_url())

    def form_invalid(self, form):
        """If the form is invalid, render the invalid form."""
        return self.render_to_response(self.get_context_data(form=form))

    def get_context_data(self, **kwargs):
        """Insert the form into the context dict."""
        if 'form' not in kwargs:
            kwargs['form'] = self.get_form()
        return super().get_context_data(**kwargs)