[#2632] fix recursion error

src/openforms/data_removal/tests/test_tasks.py

@@ -1,10 +1,13 @@
 from datetime import timedelta
 
 from django.core.exceptions import ObjectDoesNotExist
-from django.test import TestCase
+from django.test import TestCase, tag
 from django.utils import timezone
 
+from freezegun import freeze_time
+
 from openforms.config.models import GlobalConfiguration
+from openforms.forms.models.form_step import FormStep
 from openforms.forms.tests.factories import (
     FormDefinitionFactory,
     FormFactory,
@@ -57,6 +60,32 @@ def test_successful_submissions_correctly_deleted(self):
         with self.assertRaises(ObjectDoesNotExist):
             submission_to_be_deleted.refresh_from_db()
 
+    @tag("gh-2632")
+    def test_delete_successful_submission_with_deleted_form_step(self):
+        config = GlobalConfiguration.get_solo()
+
+        # submission to be deleted
+        before_limit = timezone.now() - timedelta(
+            days=config.successful_submissions_removal_limit + 1
+        )
+        with freeze_time(before_limit):
+            sub = SubmissionFactory.create(completed=True)
+
+        # create a form step to then delete which introduces the RecursionError
+        form_step = FormStepFactory.create(form=sub.form)
+        SubmissionStepFactory.create(submission=sub, form_step=form_step)
+
+        # delete form step - this causes the recursion error
+        form_step.delete()
+
+        assert sub.submissionstep_set.count() == 1
+        assert isinstance(sub.submissionstep_set.get().form_step, FormStep)
+        assert not FormStep.objects.exists()
+
+        delete_submissions()
+
+        self.assertFalse(Submission.objects.exists())
+
     def test_successful_submissions_with_form_settings_override_global_configuration(
         self,
     ):

src/openforms/submissions/models/submission_step.py

@@ -129,16 +129,37 @@ class Meta:
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
-        # load the form step from historical data if the FK has been broken (due to a
-        # deleted form step in the form designer/import functionality)
-        if not self.form_step_id:
-            self.form_step = self._load_form_step_from_history()
+        # See #2632, and a long story here on what happens:
+        #
+        # When the Submission queryset is deleted, this happens through the
+        # django.db.models.deletion.Collector which takes care of finding all related
+        # objects to manage the cascade delete.
+        #
+        # It does this (apparently) in an optimized way where only the primary keys of
+        # records (SubmssionStep in this case) are being loaded (via
+        # ``get_candidate_relations_to_delete`` and Collector.related_objects). The
+        # details are not exactly clear, but it *appears* that the form_step_id
+        # field/description is deferred. This means that when you *access* this field,
+        # Django will actually perform a separate query to load the (full) record with
+        # the additional information from the database row, which in turn leads to a new
+        # instance of the model being created, which in turn causes the __init__ method
+        # to be called again and that cycle then repeats (since that field is probably
+        # again deferred?).
+        #
+        # We can check if the field was loaded or not by checking in self.__dict__. Note
+        # that this is far from public API and a structural fix is still recommended.
+        if "form_step_id" in self.__dict__:
+            # load the form step from historical data if the FK has been broken (due to a
+            # deleted form step in the form designer/import functionality)
+            if not self.form_step_id:
+                self.form_step = self._load_form_step_from_history()
 
     def __str__(self):
         return f"SubmissionStep {self.pk}: Submission {self.submission_id} submitted on {self.created_on}"
 
     def _load_form_step_from_history(self):
         history = deepcopy(self.form_step_history)
+
         if not history:
             return None