Avoid a TypeError when ChoiceFilter choices are a callable

drf_spectacular/contrib/django_filters.py

@@ -140,7 +140,11 @@ def resolve_filter_field(self, auto_schema, model, filterset_class, field_name,
         # enrich schema with additional info from filter_field
         enum = schema.pop('enum', None)
         if 'choices' in filter_field.extra:
-            enum = [c for c, _ in filter_field.extra['choices']]
+            if callable(filter_field.extra['choices']):
+                # choices function may utilize the DB, so refrain from actually calling it.
+                enum = None
+            else:
+                enum = [c for c, _ in filter_field.extra['choices']]
         if enum:
             schema['enum'] = sorted(enum, key=str)
 

tests/contrib/test_django_filters.py

@@ -14,8 +14,8 @@
 
 try:
     from django_filters.rest_framework import (
-        AllValuesFilter, BaseInFilter, BooleanFilter, CharFilter, DjangoFilterBackend, FilterSet,
-        ModelChoiceFilter, ModelMultipleChoiceFilter, MultipleChoiceFilter, NumberFilter,
+        AllValuesFilter, BaseInFilter, BooleanFilter, CharFilter, ChoiceFilter, DjangoFilterBackend,
+        FilterSet, ModelChoiceFilter, ModelMultipleChoiceFilter, MultipleChoiceFilter, NumberFilter,
         NumericRangeFilter, OrderingFilter, RangeFilter, UUIDFilter,
     )
 except ImportError:
@@ -30,6 +30,7 @@ def init(self, **kwargs):
             pass
 
     CharFilter = NumberFilter
+    ChoiceFilter = NumberFilter
     OrderingFilter = NumberFilter
     BaseInFilter = NumberFilter
     BooleanFilter = NumberFilter
@@ -117,6 +118,10 @@ class ProductFilter(FilterSet):
         RangeFilter(field_name='price_vat')
     )
 
+    def get_choices(*args, **kwargs):
+        return (('A', 'aaa'),)
+    cat_callable = ChoiceFilter(field_name="category", choices=get_choices)
+
     class Meta:
         model = Product
         fields = [
@@ -218,6 +223,9 @@ def test_django_filters_requests(no_warnings):
     response = APIClient().get('/api/products/?multi_cat=A&multi_cat=B')
     assert response.status_code == 200, response.content
     assert len(response.json()) == 1
+    response = APIClient().get('/api/products/?cat_callable=A')
+    assert response.status_code == 200, response.content
+    assert len(response.json()) == 1
 
 
 @pytest.mark.contrib('django_filter')

tests/contrib/test_django_filters.yml

@@ -12,6 +12,11 @@ paths:
         schema:
           type: number
           format: double
+      - in: query
+        name: cat_callable
+        schema:
+          type: string
+        description: some category description
       - in: query
         name: category
         schema: