I’m struggling around Django form. I’m not really comfortable with this part of the framework.
Here is the case. I have a ModelForm containing a OneToOneField. I would like to prepopulated the ModelChoice Field with the object referenced in the URL. Ex: catalogue/location/add/7 to add a location to the product with pk=7
NB: if the PK is not included, the form is just not prefilled

models.py

class Product(models.Model):
   pass

class ProductLocation(geo_models.Model):
   product = geo_models.OneToOneField(Product, verbose_name=_('Product'), on_delete=geo_models.CASCADE, null=True,)
   geo_point = geo_models.PointField(verbose_name=_('Location'), blank=True)
   address = geo_models.CharField(verbose_name=_('Address'), max_length=255)

urls.py

urls += [
            re_path(r"^location/add/(?P<product_pk>d+)/$",
                 self.add_update_location.as_view(),
                 name='catalogue-product-location-add'),  # Prepopulate product ModelChoiceField

            path("location/add",
                 self.add_update_location.as_view(),
                 name='catalogue-location-create'  # Empty product ModelChoiceField
                 ),

            path("location/<int:pk>",
                 self.add_update_location.as_view(),
                 name='catalogue-location-update')  # Edit an existing Location
        ]

views.py

class LocationCreateUpdateView(generic.UpdateView):
    form_class = ProductLocationForm

    creating = True
    product = None

    def get_object(self, queryset=None):
        """
        Extend the role of get_object to retrieve the product specified in the url
        """
        self.creating = "pk" not in self.kwargs
        if self.creating:
            if self.kwargs.get("product_pk"):
                self.product = get_object_or_404(Product, pk=self.kwargs["product_pk"])
            return None
        else:
            return super().get_object(queryset)

# Try this way
    def get_form_kwargs(self):
        kwargs = super().get_form_kwargs()
        if self.product and not self.request.POST.get('product'):
            kwargs["product"] = self.product
        return kwargs

# Or this way
    def get_initial(self):
        initial = super().get_initial()
        if self.product:
            initial["product"] = self.product
        return initial

forms.py

class ProductLocationForm(forms.ModelForm):
    def __init__(self, product=None, instance=None, *args, **kwargs):
        # I tried this
        if not instance and product:
            instance = ProductLocation(product=product)
        super().__init__(instance=instance, *args, **kwargs)

I tried to override get_initial() to pass the product to the form didn’t validate, ask to select a product in the list and moreover, it erase the inital value.

I also use get_form_kwargs() to pass the product to the form init function and try to :

• attach the product to the ProductLocation instance
• set inital data in the init
• set self.fidels['product'].initial = product

Thanks for your help

PS : some references on SO

• Pass initial value to a modelform in django
• How to instantiate a Django ModelForm with pre-filled required fields?
• Set initial value in django model form