Django CreateView with get_success_url 不适用于此特定情况

Question

I'm using Django 2.1. I'm having a problem with a CreateView because I need to redirect to the update url, but that url contains one argument that is created manually after verifying that the form is valid.

This is the view code:

class ProjectCreateInvestmentCampaignView(LoginRequiredMixin, SuccessMessageMixin, generic.CreateView):
    template_name = 'webplatform/project_edit_investment_campaign.html'
    model = InvestmentCampaign
    form_class = CreateInvestmentCampaignForm
    success_message = 'Investment campaign created!'

    def get_success_url(self):
        return reverse_lazy('project-update-investment-campaign',
                            args=(self.kwargs['pk'], self.object.campaign.pk, self.object.pk))

    def form_valid(self, form):
        project = Project.objects.get(pk=self.kwargs['pk'])
        form.instance.investment_type = "A"
        form.instance.contract_type = "CI"
        form.instance.history_change_reason = 'Investment campaign created'
        valid = super(ProjectCreateInvestmentCampaignView, self).form_valid(form)
        if valid:
            campaign = CampaignBase.objects.create(project=project, )
            form.instance.campaign = campaign
            form.instance.campaign.project = project
            form.instance.campaign.creation_date = timezone.now()
            form.save()
        return valid

As you can see, on the form_valid I validate first the form, and then I create the object campaign and assign all the related data. This is working fine. The problem came when I changed the get_success_url to fit my use case, that is redirecting to the update view. I debugged and saw that at the moment I create the variable valid on the form_valid , it checks the success url, and that triggers me the following error:

Exception Type: AttributeError
Exception Value:    
'NoneType' object has no attribute 'pk'
Exception Location: /Volumes/Archivos/work/i4b/webplatform/views/investor_campaign_views.py in get_success_url, line 25

I asume that the error is because the campaign is not created yet so it's trying to get the pk from a non existing object.

The thing is that I cannot create the campaign if the form is not validated, but I need the campaign to make the url working (that url is working as it is on the UpdateView that I already have).

Answer 1

It will only invoke get_success_url after form_valid . So it's up to form_valid to create and save the objects needed. If it's valid for them not to be created, you need a different approach. Maybe initialize (say) self.campaign_pk = 0 , update it if a campaign can be created with the pk of the campaign object, and let the next view sort out what to do when pk==0. Or,

...
    args=(self.kwargs['pk'], 
          self.object.campaign.pk if self.object.campaign else 0, 
          self.object.pk))

(I don't fully follow your code so I might be barking up the wrong tree here)

It may be that you don't want CreateView but FormView , which doesn't handle object creation for you, so you may find greater flexibility over how to process a valid form that nevertheless cannot be fully honoured all the time. Or even, just a plain old function-based view, in which you can process two or more forms and be far more able to decide on conditions that constitute non-validity even after all the forms have technically validated.

This is a function-based view structure I have used where I have two forms to process, and a fairly long but boring set of operations to do after BOTH forms validate:

def receive_view( request):

    # let's put form instantiation in one place not two, and reverse the usual test. This
    # makes for a much nicer layout with actions not sandwiched by "boilerplate" 
    # note any([ ]) forces invocation of both .is_valid() methods 
    # so errors in second form get shown even in presence of errors in first

    args = [request.POST, ] if request.method == "POST" else []
    batchform = CreateUncWaferBatchForm( *args, layout=CreateUncWaferBatchLayout )
    po_form =  CreateUncWaferPOForm(     *args, layout = CreateUncWaferPOLayout, prefix='po')
    if request.method != "POST" or any(  
        [ not batchform.is_valid(), not po_form.is_valid() ]):

        return render(request, 'wafers/receive_uncoated.html',   # can get this out of the way at the top
            {'batchform': batchform,  
            'po_form': po_form, 
        })

    #it's a POST, everything is valid, do the work
    ...
    return redirect('appname:viewname', ...)

Answer 2

For me, get_success_url was not invoked as the form was not valid (was invalid ) and I didn't know. You can override form_invalid(self, form) to control the behavior.

Also, consider this block of code to show any errors in your template

{% if form.errors %}
<div class="alert alert-danger" role="alert">
    {% for field, errors in form.errors.items %}
    {% for error in errors %}
    <b>{{ field }}</b>: {{ error }}
    {% endfor %}
    {% endfor %}
</div>
{% endif %}