Django CBV - dealing with optional parameters in URLs - django

Question

I have a Class Based View to list animals from a specific herd. There are multiple herds, so the user can either see all animals from ONE herd, or all animals from ALL herds.
How do I have an optional URL parameter and handle it in the CBV?
urls:
url(r'list/(?P<hpk>[0-9]+)/$', AnimalList.as_view(), name = 'animal_list'),
url(r'list/$', AnimalList.as_view(), name = 'animal_list'),
My view:
class AnimalList(ListView):
model = Animal
def get_queryset(self):
if self.kwargs is None:
return Animal.objects.all()
return Animal.objects.filter(herd = self.kwargs['hpk']) # <--- line 19 that returns an error
Going to a URL of like /animals/list/3/ works fine, while /animals/list/ fails with an error. Here's that error:
KeyError at /animals/list/
'hpk'
Request Method: GET
Request URL: http://localhost:8000/animals/list/
Django Version: 1.8.2
Exception Type: KeyError
Exception Value:
'hpk'
Exception Location: /var/www/registry/animals/views.py in get_queryset, line 19
I get that the self.kwargs is a dictionary, and when I print() it inside the view, it'll show it's empty. But I can't figure out how to capture that scenario. I feel like this is a simple, stupid error I'm missing.

Answer 1

To anyone who may stumble on this and need an answer, here is my working code after figuring it out:
class AnimalList(ListView):
model = Animal
def get_queryset(self):
if 'hpk' in self.kwargs:
return Animal.objects.filter(herd = self.kwargs['hpk'])
return Animal.objects.all()
Essentially we test to see if the URL parameter hpk is present in the list of self.kwargs. If it is, we filter the queryset. Otherwise, we return all animals.
Hope this helps someone :)

Answer 2

I would implement this using GET parameters instead of separate URLs. With this approach, there is only one URL /list/ that is filtered by parameters, for example /list/?hpk=1.
This is more flexible as you can eventually add more queries /list/?hpk=1&origin=europe
#url(r'list/$', AnimalList.as_view(), name = 'animal_list'),
class AnimalList(ListView):
model = Animal
def get_queryset(self):
queryset = Animal.objects.all()
hpk = self.request.GET.get("hpk"):
if hpk:
try:
queryset = queryset.filter(herd=hpk)
except:
# Display error message
return queryset