Pass a dict as data to django-filter

In order to filter with multivalue params such as 'in' lookups there are two alternatives:

* ?multiparam=1,2,3
* ?multiparam=1&multiparam=2

The second option is a better approach when facing strings. However, by definition QueryDict does only take into account the last param included.

Django-filters expect a dict as data. To be congruent with what is passed in the request we need to transform `query_params` to a `dict`.

As can be seen in the test written, adhoc programming must be done also in django-filter to allow 'in' lookups but that's another issue.

Part of the solution was taken from @leo-the-manic in http://stackoverflow.com/questions/13349573/how-to-change-a-django-querydict-to-python-dict#answer-22100334

rest_framework/filters.py

@@ -65,7 +65,11 @@ class DjangoFilterBackend(BaseFilterBackend):
         filter_class = self.get_filter_class(view, queryset)
 
         if filter_class:
-            return filter_class(request.query_params, queryset=queryset).qs
+            # Using solution by @leo-the-manic goo.gl/3LoFIj
+            return filter_class(
+                {k: v[0] if len(v) == 1 else v for k, v in request.query_params.lists()},
+                queryset=queryset
+            ).qs
 
         return queryset
 

tests/test_filters.py

@@ -34,11 +34,17 @@ if django_filters:
     class SeveralFieldsFilter(django_filters.FilterSet):
         text = django_filters.CharFilter(lookup_type='icontains')
         decimal = django_filters.NumberFilter(lookup_type='lt')
+        decimal_in = django_filters.MethodFilter(action="filter_decimal_in")
         date = django_filters.DateFilter(lookup_type='gt')
 
         class Meta:
             model = FilterableItem
-            fields = ['text', 'decimal', 'date']
+            fields = ['text', 'decimal', 'decimal_in', 'date']
+
+        def filter_decimal_in(self, qs, values):
+            if not hasattr(values, '__iter__'):
+                values = (values,)
+            return qs.filter(decimal__in=values)
 
     class FilterClassRootView(generics.ListCreateAPIView):
         queryset = FilterableItem.objects.all()
@@ -207,6 +213,16 @@ class IntegrationTestFiltering(CommonFilteringTestCase):
         expected_data = [f for f in self.data if Decimal(f['decimal']) < search_decimal]
         self.assertEqual(response.data, expected_data)
 
+        # Tests that the decimal_in filter set with 'in' in the filter class works
+        search_decimal_in = ['1.25', '2.25']
+        request = factory.get('/', {
+            'decimal_in': search_decimal_in,
+        })
+        response = view(request).render()
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        expected_data = [f for f in self.data if f['decimal'] in search_decimal_in]
+        self.assertEqual(response.data, expected_data)
+
         # Tests that the date filter set with 'gt' in the filter class works.
         search_date = datetime.date(2012, 10, 2)
         request = factory.get('/', {'date': '%s' % search_date})  # search_date str: '2012-10-02'