class InvoiceViewSet(viewsets.ViewSet):
    serializer_class = InvoiceSerializer
    filter_backend = filters.DjangoFilterBackend
    filter_fields = ('status','supplier',)

    def list(self,request,):
        queryset = Invoice.objects.filter()
        serializer = InvoiceSerializer(queryset, many=True)
        return Response(serializer.data)

    def retrieve(self, request, pk=None):
        queryset = Invoice.objects.filter()
        invoice = get_object_or_404(queryset, pk=pk)
        serializer = InvoiceSerializer(invoice)
        return Response(serializer.data)

class InvoiceItemViewSet(viewsets.ViewSet):

    serializer_class = InvoiceItemSerializer

    def list(self,request,invoice_pk=None):
        queryset = InvoiceItem.objects.filter(invoice=invoice_pk)
        serializer = InvoiceItemSerializer(queryset,many=True)
        return Response(serializer.data)


    def retrieve(self,request,pk,invoice_pk):
        queryset = InvoiceItem.objects.filter(pk=pk,invoice=invoice_pk)
        invoice_item = get_object_or_404(queryset,pk=pk)
        serializer = InvoiceItemSerializer(invoice_item)
        return Response(serializer.data)

from django.conf.urls import url, include
#viewset
from rest_framework_nested import routers
from payables.views import InvoiceViewSet,InvoiceItemViewSet

router = routers.SimpleRouter()
router.register(r'invoices', InvoiceViewSet,base_name='invoices')

invoice_item_router = routers.NestedSimpleRouter(router,r'invoices',lookup='invoice')
invoice_item_router.register(r'items', InvoiceItemViewSet, base_name='invoice_items')

urlpatterns = [
    url(r'^',include(router.urls)),
    url(r'^',include(invoice_item_router.urls))
    ]

queryset = Invoice.objects.filter()