apps/budgeting: add API filters for categories and is_archived

add category=<category_pk> and / or is_archived=true or false as url parameter
to get all propsals, either remove the parameter or add it as empty parameter "category="

meinberlin/apps/budgeting/api.py

@@ -6,6 +6,7 @@
 
 from adhocracy4.api.mixins import ModuleMixin
 from adhocracy4.api.permissions import ViewSetRulesPermission
+from meinberlin.apps.contrib.filters import IdeaCategoryFilterBackend
 
 from .models import Proposal
 from .serializers import ProposalSerializer
@@ -32,8 +33,9 @@ class ProposalViewSet(ModuleMixin,
     serializer_class = ProposalSerializer
     permission_classes = (ViewSetRulesPermission,)
     filter_backends = (DjangoFilterBackend,
-                       OrderingFilter,)
-    # filter_fields = ('is_archived',)
+                       OrderingFilter,
+                       IdeaCategoryFilterBackend,)
+    filter_fields = ('is_archived', 'category',)
     ordering_fields = ('created',
                        'comment_count',
                        'positive_rating_count',)

meinberlin/apps/contrib/filters.py

@@ -1,4 +1,5 @@
 from django.utils.translation import gettext_lazy as _
+from rest_framework.filters import BaseFilterBackend
 
 from adhocracy4.filters.filters import DistinctOrderingFilter
 from adhocracy4.filters.widgets import DropdownLinkWidget
@@ -19,3 +20,15 @@ def __init__(self, *args, **kwargs):
             kwargs['widget'] = OrderingWidget
         kwargs['empty_label'] = None
         super().__init__(*args, **kwargs)
+
+
+class IdeaCategoryFilterBackend(BaseFilterBackend):
+    """Filter ideas for the categories in API."""
+
+    def filter_queryset(self, request, queryset, view):
+
+        if 'category' in request.GET:
+            category = request.GET['category']
+            return queryset.filter(category=category)
+
+        return queryset