Question

I have 2 models which are related to each other using One to One Relation. How can i display the validation error if object of one model is already related to another.

Suppose i have 2 models

   Class Place(models.Model):
        field1 = CharField()
        field2 = CharField()

   Class Restaurant(models.Model):
       related_field = OneToOneField(Place)
       field3 = CharField()

In my case For one place one Restaurant. If user submits new Restaurant for the same place, then a validation should raise

If Restaurant object already attached to Place object, so for second Restaurant for same Place object i want to display validation

In admin we usually see this message “Restaurent with this Place already exists.” But how can i achieve the same this using modelform with generic views

 class RestaurantCreateView(CreateView):
       form_class = RestaurantForm
       template_name = 'restaurant_create.html'

       def get_success_url(self):
           return reverse_lazy('restuarants', args=[self.object.id])

       def get_place(self, **kwargs):
           id = self.kwargs['pk']
           place = Place.objects.get(id=id)
           return place 

       def get_context_data(self, **kwargs):
           context = super(RestaurantCreateView, self).get_context_data(**kwargs)
           place = self.get_place()
           context['place'] = place
           return context

       def form_valid(self, form):
          self.object = form.save(commit=False)
          place = self.get_place()
          self.object.place = place
          self.object.save()
          return HttpResponseRedirect(self.get_success_url())

How can perform One To One relation validation in class based generic views?

Answer 1

Then you need to pass the Place object into your Restaurant form. The form validation has no access to these things defined in the view unless you explicitly pass it that data.

class MyForm(forms.ModelForm):
    class Meta:
         model = Restaurant

    def __init__(self, *args, **kwargs):
        self.place = kwargs.pop('place', None)
        super(MyForm, self).__init__(*args, **kwargs

    def clean_related_field(self):
        place = self.place
        try:
            place.restaurant
        except Restaurant.DoesNotExist:
            return place
        raise forms.ValidationError("Restaurant already exists for that book")


class MyView(...):
    form_class = MyForm

    def get_form_kwargs(self):
        kwargs = super(MyView, self).get_form_kwargs()
        kwargs['place'] = Place.objects.get(id=self.kwargs['pk'])
        return kwargs

{% if form.related_field.errors %}.........{% endif %}

Another approach is to fake validation in form_valid() and set the errors dict, and return the response. This method may be preferable since it’s much more contained. Also especially if you are not using the form field anyways, you might as well add an error flag to the context.

class MyView():
    def form_valid(self, form):
        if Restaurant.objects.filter(related_field=self.get_place()):
            ctx = self.get_context_data(form=form)
            ctx['massive_error'] = True
            return self.render_to_response(ctx)