Fix filtering of object-type custom fields when "is empty" is selected (#21829)

netbox/utilities/forms/widgets/modifiers.py

@@ -48,11 +48,13 @@ class FilterModifierWidget(forms.Widget):
             Just the value string for form validation. The modifier is reconstructed
             during rendering from the query parameter names.
         """
-        # Special handling for empty - check if field__empty exists
+        # Special handling for empty modifier: return None so the underlying field does not
+        # attempt to validate 'true'/'false' as a field value (e.g. a model PK). The
+        # `__empty` query parameter is consumed directly by the filterset and by
+        # `applied_filters`, so no value from the field itself is needed here.
         empty_param = f"{name}__empty"
         if empty_param in data:
-            # Return the boolean value for empty lookup
-            return data.get(empty_param)
+            return None
 
         # Try exact field name first
         value = self.original_widget.value_from_datadict(data, files, name)
@@ -113,8 +115,13 @@ class FilterModifierWidget(forms.Widget):
                     # Build a minimal choice list with just the selected values
                     choices = []
                     if pk_values:
-                        selected_objects = original_choices.queryset.filter(pk__in=pk_values)
-                        choices = [(obj.pk, str(obj)) for obj in selected_objects]
+                        try:
+                            selected_objects = original_choices.queryset.filter(pk__in=pk_values)
+                            choices = [(obj.pk, str(obj)) for obj in selected_objects]
+                        except (ValueError, TypeError):
+                            # pk_values may contain non-PK strings (e.g. 'true'/'false' from the
+                            # empty modifier); silently skip rendering selected choices in that case.
+                            pass
 
                     # Re-add the "None" option if it was selected via the null choice value
                     if settings.FILTERS_NULL_CHOICE_VALUE in values:

netbox/utilities/templatetags/helpers.py

@@ -491,6 +491,35 @@ def applied_filters(context, model, form, query_params):
             'link_text': link_text,
         })
 
+    # Handle empty modifier pills separately. `FilterModifierWidget.value_from_datadict()`
+    # returns None for fields with a `field__empty` query parameter so that the underlying
+    # form field does not attempt to validate 'true'/'false' as a real field value (which
+    # would raise a ValidationError for ModelChoiceField). Because the value is None, these
+    # fields never appear in `form.changed_data`, so we build their pills directly from the
+    # query parameters here.
+    for param_name, param_value in query_params.items():
+        if not param_name.endswith('__empty'):
+            continue
+        field_name = param_name[:-len('__empty')]
+        if field_name not in form.fields or field_name == 'filter_id':
+            continue
+
+        querydict = query_params.copy()
+        querydict.pop(param_name)
+        label = form.fields[field_name].label or field_name
+
+        if param_value.lower() in ('true', '1'):
+            link_text = f'{label} {_("is empty")}'
+        else:
+            link_text = f'{label} {_("is not empty")}'
+
+        applied_filters.append({
+            'name': param_name,
+            'value': param_value,
+            'link_url': f'?{querydict.urlencode()}',
+            'link_text': link_text,
+        })
+
     save_link = None
     if user.has_perm('extras.add_savedfilter') and 'filter_id' not in context['request'].GET:
         object_type = ObjectType.objects.get_for_model(model).pk

netbox/utilities/tests/test_filter_modifiers.py

@@ -6,8 +6,11 @@ from django.template import Context
 from django.test import RequestFactory, TestCase
 
 import dcim.filtersets  # noqa: F401 - Import to register Device filterset
-from dcim.forms.filtersets import DeviceFilterForm
-from dcim.models import Device
+from core.models import ObjectType
+from dcim.forms.filtersets import DeviceFilterForm, SiteFilterForm
+from dcim.models import Device, Manufacturer, Site
+from extras.choices import CustomFieldTypeChoices
+from extras.models import CustomField
 from netbox.filtersets import BaseFilterSet
 from tenancy.models import Tenant
 from users.models import User
@@ -338,3 +341,70 @@ class EmptyLookupTest(TestCase):
         self.assertGreater(len(result['applied_filters']), 0)
         filter_pill = result['applied_filters'][0]
         self.assertIn('not empty', filter_pill['link_text'].lower())
+
+
+class ObjectCustomFieldEmptyLookupTest(TestCase):
+    """
+    Regression test for https://github.com/netbox-community/netbox/issues/21535.
+
+    Rendering a filter form with an object-type custom field and the __empty modifier
+    must not raise a ValueError or produce a form validation error.
+    Filter pills must still appear for the empty modifier.
+    """
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.user = User.objects.create(username='test_user_obj_cf')
+        site_type = ObjectType.objects.get_for_model(Site)
+        cf = CustomField(
+            name='test_obj_cf',
+            type=CustomFieldTypeChoices.TYPE_OBJECT,
+            related_object_type=ObjectType.objects.get_for_model(Manufacturer),
+        )
+        cf.save()
+        cf.object_types.set([site_type])
+
+    def _make_form_and_result(self, querystring):
+        query_params = QueryDict(querystring)
+        form = SiteFilterForm(query_params)
+        request = RequestFactory().get('/', query_params)
+        request.user = self.user
+        context = Context({'request': request})
+        result = applied_filters(context, Site, form, query_params)
+        return form, result
+
+    def test_render_form_with_empty_true_no_error(self):
+        """Rendering SiteFilterForm with cf__empty=true must not raise ValueError."""
+        query_params = QueryDict('cf_test_obj_cf__empty=true')
+        form = SiteFilterForm(query_params)
+        try:
+            str(form['cf_test_obj_cf'])
+        except ValueError as e:
+            self.fail(f"Rendering object-type custom field with __empty=true raised ValueError: {e}")
+
+    def test_render_form_with_empty_false_no_error(self):
+        """Rendering SiteFilterForm with cf__empty=false must not raise ValueError."""
+        query_params = QueryDict('cf_test_obj_cf__empty=false')
+        form = SiteFilterForm(query_params)
+        try:
+            str(form['cf_test_obj_cf'])
+        except ValueError as e:
+            self.fail(f"Rendering object-type custom field with __empty=false raised ValueError: {e}")
+
+    def test_no_validation_error_on_empty_true(self):
+        """The filter form must not have a validation error for the field when __empty=true."""
+        form, _ = self._make_form_and_result('cf_test_obj_cf__empty=true')
+        form.is_valid()
+        self.assertNotIn('cf_test_obj_cf', form.errors)
+
+    def test_filter_pill_appears_for_empty_true(self):
+        """A filter pill showing 'is empty' must be generated for an object-type CF with __empty=true."""
+        _, result = self._make_form_and_result('cf_test_obj_cf__empty=true')
+        self.assertGreater(len(result['applied_filters']), 0)
+        self.assertIn('empty', result['applied_filters'][0]['link_text'].lower())
+
+    def test_filter_pill_appears_for_empty_false(self):
+        """A filter pill showing 'is not empty' must be generated for an object-type CF with __empty=false."""
+        _, result = self._make_form_and_result('cf_test_obj_cf__empty=false')
+        self.assertGreater(len(result['applied_filters']), 0)
+        self.assertIn('not empty', result['applied_filters'][0]['link_text'].lower())