title: Django not getting id from the url parameter
body: <p>i have these serializer on Django</p>
  <pre><code>class CarManagerSerializer(serializers.ModelSerializer):
  
      class Meta:
          model = Manager
          fields = '__all__'
  </code></pre>
  <p>and this view class</p>
  <pre><code>class CarManagerViewSet(APIView):
      allowed_methods = ('GET',)
  
      def get(self, request, manager_id = None):
          if manager_id is None:
              managers = Manager.objects.all().order_by('-name')
              serializer = CarManagerSerializer(managers , many=True)
              serializer_data = serializer.data
              return Response(serializer_data, status=status.HTTP_200_OK)
          else:
              managers = Manager.objects.get(id = manager_id).select_related('cars')
              serializer = CarManagerSerializer(managers , many=True)
              serializer_data = serializer.data
              return Response(serializer_data, status=status.HTTP_200_OK)
  </code></pre>
  <p>im trying to get the manager by its manager id</p>
  <pre><code>http://127.0.0.1:8000/carmanagers/3
  </code></pre>
  <p>but the manager_id wont get passed to the view, i keep getting 'None'
  where did i miss ?
  below is the url</p>
  <pre><code>urlpatterns = [
      url(
          r'carmanagers/(?P&lt;manager_id&gt;[0-9]+)/$',
          CarManagerViewSet.as_view(),
          name='car-managers'
      ),
      url(
        r'carmanagers',
        CarManagerViewSet.as_view(),
        name='car-managers'
      ),
  ]
  </code></pre>