improve Django Doc with an example for formfield_for_foreignkey accessing parent ID

[anonymous]

Please,
Could you add an example for formfield_for_foreignkey (
​https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.formfield_for_foreignkey) showing how to access parent ID for filtering a foreignkey.

I saw on ​http://www.stereoplex.com/blog/filtering-dropdown-lists-in-the-django-admin

parent_id = request.META['PATH_INFO'].strip('/').split('/')[-1]

Clearly it's not ideal.

Thanks!

[Aymeric Augustin]

Could you explain a bit more what you're trying to achieve?

To help you, we need something like: "here's my models definition, here's my admin definiton, at this URL ... I would like to..."

[Tim Graham]

The request is a documentation additional as outlined in the blog post.

It would be nice if there were a cleaner way to achieve the filtering, but until then, I guess we can document this solution.

[Tim Graham]

​PR

[Tim Graham]

Left comments for improvement.

[Tobias Kunze]

For reference, the blog post referred to in the original issue can be found ​on the web archive, and the relevant code reads like this:

class MountaineeringInfoInline(admin.TabularInline):
    model = MountaineeringInfo
    formset = MountaineeringInfoInlineFormset

    def formfield_for_dbfield(self, field, **kwargs):
        if field.name == 'area':
            # Note - get_object hasn't been defined yet
            parent_trip = self.get_object(kwargs['request'], Trip)
            contained_areas = Area.objects.filter(area__contains=parent_trip.area.area)
            return forms.ModelChoiceField(queryset=contained_areas)
        return super(MountaineeringInfoInline, self).formfield_for_dbfield(field, **kwargs)

    def get_object(self, request, model):
        object_id = request.META['PATH_INFO'].strip('/').split('/')[-1]
        try:
            object_id = int(object_id)
        except ValueError:
            return None
        return model.objects.get(pk=object_id)

At least mentioning formfield_for_dbfield in the docs at all, anywhere, sounds like a good idea to me, regardless of the specifics on how to get the current pk or instance.

[Caio Ariede]

​PR

[Mariusz Felisiak]

​New PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In d38c3411:

Fixed #21528 -- Added note about filtering form field's queryset based on instance to admin docs.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 7fe7d832:

[3.1.x] Fixed #21528 -- Added note about filtering form field's queryset based on instance to admin docs.

Backport of d38c34119e91a533c797098f150abe99b5ee2fd8 from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In 96b04f5:

[3.0.x] Fixed #21528 -- Added note about filtering form field's queryset based on instance to admin docs.

Backport of d38c34119e91a533c797098f150abe99b5ee2fd8 from master