Using same lookup kwarg for base and nested views

[Kangaroux]

Suppose I have a resource company with a nested resource users:

/company/<pk>
/company/<company_pk>/users

I rely on the company_pk kwarg to check if request.user has permissions, but because the naming is different, I need to create two permission classes: one for nested views and one for the base resource.

I tried setting lookup_url_kwarg = "company_pk" on the CompanyViewSet but that generates the nested routes with company_company_pk. Setting lookup="" on the router generates _company_pk.

It's not a big deal to create a couple extra permission classes, or to make a custom router that generates the nested lookups like I want, but I wanted to know if this is possible with the library as-is

[alanjds]

Hi, @Kangaroux. Thanks for reaching out.

I see what you mean, but I did not knew that it leads to the need to create two permission classes :/
And by heart I did not remember if there is a way to enforce the url var you want. Sorry for it.

I will take a look on the DRF docs and if I find something I ping you. For today, no I have not a better idea 🤷.

[alanjds]

Hey @Kangaroux, I got some more understanding over the lookup value.

First, the lookup name cames from this pieces of code:

• On DRF: https://github.com/encode/django-rest-framework/blob/fd8adb32cec9c7545039f03cc3aa6cda95d4d692/rest_framework/routers.py#L205-L226
• On drf-nested-routers (this repo):

  drf-nested-routers/rest_framework_nested/routers.py

  Lines 48 to 53 in 4c3d7d3

  	class NestedMixin(object):
  	def __init__(self, parent_router, parent_prefix, *args, **kwargs):
  	self.parent_router = parent_router
  	self.parent_prefix = parent_prefix
  	self.nest_count = getattr(parent_router, 'nest_count', 0) + 1
  	self.nest_prefix = kwargs.pop('lookup', 'nested_%i' % self.nest_count) + '_'

If you really want to get rid of the company_ thing on the nested resource, you can play with the .nest_prefix attribute of the nested router. Yet I do not guarantee that there will be no side-effects, nor that the stuff will not break.

Conceptually, the parent lookup is about how to get the parent object from the child object!

I mean:

# models.py
class Company(models.Model):
    ...

class User(models.Model):
    company = models.ForeignKey('Company', ...)

That would make sense to produce:

/company/<pk>/
/company/<company_pk>/users/<pk>/

As it ease the task to reach the Company from the User inside the View:

User.objects.get(company_pk=self.kwargs['company_pk'], pk=self.kwargs['pk'])
# or more generically:
User.objects.get(**self.kwargs)

Also, in the View for /company/<company_pk>/users/<pk>/ the .get_object() is implemented by default by DRF like:

        filter_kwargs = {self.lookup_field: self.kwargs[lookup_url_kwarg]}
        obj = get_object_or_404(queryset, **filter_kwargs)

then the <company_pk> is just unused.

Hope this to helps to understand how and why things are as they are today, yet any change proposal will be very welcome from my side 👍

Thanks again,
Best regards.