Run QuestionAssignment's delete garbage collection in signal

evap/evaluation/models.py

@@ -23,6 +23,7 @@
 from django.db import IntegrityError, models, transaction
 from django.db.models import CheckConstraint, Count, Exists, F, Manager, OuterRef, Q, QuerySet, Subquery, Value
 from django.db.models.functions import Coalesce, Lower, NullIf, TruncDate
+from django.db.models.signals import post_delete
 from django.dispatch import Signal, receiver
 from django.http import HttpRequest
 from django.template import Context, Template
@@ -1373,18 +1374,14 @@ class Meta:
         ordering = ["order"]
         unique_together = [("question", "questionnaire")]
 
-    def delete(self, using=None, keep_parents=False) -> tuple[int, dict[str, int]]:
-        if not self.question.is_heading_question:
-            assert not self.question.answer_class.objects.filter(assignment=self).exists(), (
-                "cannot delete question with answers"
-            )
-        count = 0
-        meta: dict[str, int] = {}
 
-        if not self.question.questionnaires.exclude(pk=self.questionnaire.pk).exists():
-            count, meta = self.question.delete(using=using, keep_parents=False)  # garbage-collect unused questions
-        self_count, self_meta = super().delete(using=using, keep_parents=keep_parents)
-        return count + self_count, meta | self_meta
+@receiver(post_delete, sender=QuestionAssignment)
+@transaction.atomic
+def _question_assignment_post_delete(*, instance: QuestionAssignment, **_kwargs) -> None:
+    """Garbage-collect unused questions once no questionnaires reference them anymore."""
+
+    if not QuestionAssignment.objects.filter(question=instance.question.pk).exists():
+        Question.objects.filter(pk=instance.question.pk).delete()
 
 
 @dataclass

evap/evaluation/tests/test_models.py

@@ -17,6 +17,7 @@
     Evaluation,
     NotArchivableError,
     Question,
+    QuestionAssignment,
     Questionnaire,
     QuestionType,
     Semester,
@@ -58,14 +59,38 @@ def test_can_be_deleted_by_manager(self):
         self.assertTrue(semester.can_be_deleted_by_manager)
 
 
-class TestQuestionnaire(WebTest):
+class TestQuestionnaire(TestCase):
     def test_can_be_deleted_by_manager(self):
         questionnaire = baker.make(Questionnaire)
         self.assertTrue(questionnaire.can_be_deleted_by_manager)
 
         baker.make(Contribution, questionnaires=[questionnaire])
         self.assertFalse(questionnaire.can_be_deleted_by_manager)
 
+    def test_locked_contributor_questionnaire(self):
+        questionnaire = baker.prepare(Questionnaire, is_locked=True, type=Questionnaire.Type.CONTRIBUTOR)
+        self.assertRaises(ValidationError, questionnaire.clean)
+
+
+class TestQuestionAssignment(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.assignment = baker.make(QuestionAssignment)
+        cls.question = cls.assignment.question
+        cls.questionnaire = cls.assignment.questionnaire
+
+    def test_assignment_delete_gc(self):
+        self.assignment.delete()
+        self.assertRaises(Question.DoesNotExist, self.question.refresh_from_db)
+
+    def test_assignment_queryset_delete_gc(self):
+        QuestionAssignment.objects.filter(pk=self.assignment.pk).delete()
+        self.assertRaises(Question.DoesNotExist, self.question.refresh_from_db)
+
+    def test_questionnaire_cascading_delete_gc(self):
+        self.questionnaire.delete()
+        self.assertRaises(Question.DoesNotExist, self.question.refresh_from_db)
+
 
 @override_settings(EVALUATION_END_OFFSET_HOURS=0)
 class TestEvaluations(WebTest):
@@ -1148,9 +1173,3 @@ def test_recipient_list_filtering(self):
             evaluation, [EmailTemplate.Recipients.CONTRIBUTORS], filter_users_in_cc=True
         )
         self.assertCountEqual(recipient_list, [contributor2, contributor3])
-
-
-class QuestionnaireTests(TestCase):
-    def test_locked_contributor_questionnaire(self):
-        questionnaire = baker.prepare(Questionnaire, is_locked=True, type=Questionnaire.Type.CONTRIBUTOR)
-        self.assertRaises(ValidationError, questionnaire.clean)