如何在Django CreateView中处理错误

Question

Using Django, I have a model and a class based view based on the provided CreateView class. Everything works fine - I can have a template that renders the form, validation occurs, the data is properly saved and the success_url redirected to on completion.

The problem occurs in that I have a unique_together constraint on two of the fields. If this error is hit, it appears that form_valid() doesn't catch it, and an error page is produced instead.

My goal is to be able to catch this ahead of time and return the user to the form - with the data filled in from their last attempt - and display a message to them. Feels like this should be simple, and I added code to form_valid() in the view to identify the problem, but I have no clue what to do next.

A redirect doesn't work because I can't add the context in (or can I?) and I really don't want to put everything in the URL. Any ideas where to look?

The Model:

class Client(BaseModel):
    name = models.CharField(max_length=240, db_index=True, verbose_name='Client Name')
    organization_link = models.ForeignKey(Organization, on_delete=models.PROTECT, verbose_name='Organization')
    client_group_link = models.ForeignKey(ClientGroup, blank=True, on_delete=models.SET_NULL, null=True, verbose_name='Client Group')
    policy_link = models.ManyToManyField(OrganizationPolicy, related_name='attached_clients', verbose_name='Policies')
    active = models.BooleanField(default=True, db_index=True, verbose_name='Active')

    class Meta:
        unique_together = (('name', 'organization_link'),)

The View:

class ClientCreateView(CreateView):
    model = Client
    fields = ['name', 'client_group_link', 'active']
    success_url = reverse_lazy('entities_client_roster')

    def form_valid(self, form):
        organization = get_object_or_404(Organization, id=self.kwargs['organization'])
        form.instance.organization_link_id = organization.id
        return super().form_valid(form)

The snippet URL config:

url(r'^client_create/(?P<organization>[0-9a-f-]+)',
    ClientCreateView.as_view(template_name='entities/client_create.html'),

And the error:

IntegrityError at /accept/client_create/xxx
duplicate key value violates unique constraint "app_entities_client_name_organization_link_id_5e612e47_uniq"

Answer 1

Thanks @geckos... that pointed me in the right direction. Adding the following to my View did the job:

def post(self, request, *args, **kwargs):
    try:
        super().post(request, *args, **kwargs)
    except IntegrityError:
        messages.add_message(request, messages.ERROR,
                             'You already have registered a Client with this name. ' + \
                             'All of your Client names must be unique.')
        return render(request, template_name=self.template_name, context=self.get_context_data())