python - View didn't return an HttpResponse object. It returned None instead

Question

The view below is gives me the error when using the POST method. I'm trying to load the model data into a form, allow the user to edit, and then update the database. When I try to Save the changes I get the above error.

def edit(request, row_id):
    rating = get_object_or_404(Rating, pk=row_id)
    context = {'form': rating}
    if request.method == "POST":
        form = RatingForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('home.html')
    else:
        return render(
            request,
            'ratings/entry_def.html',
            context
        )

Here is the trace from the terminal.

[15/Apr/2016 22:44:11] "GET / HTTP/1.1" 200 1554
[15/Apr/2016 22:44:12] "GET /rating/edit/1/ HTTP/1.1" 200 919
Internal Server Error: /rating/edit/1/
Traceback (most recent call last):
   File "/Users/michelecollender/ENVlag/lib/python2.7/site-packages/django/core/handlers/base.py", line 158, in get_response
    % (callback.__module__, view_name))
ValueError: The view ratings.views.edit didn't return an HttpResponse object. It returned None instead.

Answer 1

You are redirecting if form.is_valid() but what about the form is invalid? There isn't any code that get's executed in this case? There's no code for that. When a function doesn't explicitly return a value, a caller that expects a return value is given None. Hence the error.

You could try something like this:

def edit(request, row_id):
    rating = get_object_or_404(Rating, pk=row_id)
    context = {'form': rating}
    if request.method == "POST":
        form = RatingForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect('home.html')
        else :
            return render(request, 'ratings/entry_def.html', 
                          {'form': form})
    else:
        return render(
            request,
            'ratings/entry_def.html',
            context
        )

This will result in the form being displayed again to the user and if you have coded your template correctly it will show which fields are invalid.