Handle ObjectDoesNotExist in evaluation of repr (#592)

CHANGELOG.md

@@ -12,6 +12,10 @@
 - Python: Confirm Python 3.12 support ([#572](https://github.com/jazzband/django-auditlog/pull/572))
 - feat: `thread.local` replaced with `ContextVar` to improve context managers in Django 4.2+
 
+#### Fixes
+
+- fix: Handle `ObjectDoesNotExist` in evaluation of `object_repr` ([#592](https://github.com/jazzband/django-auditlog/pull/592))
+
 ## 3.0.0-beta.2 (2023-10-05)
 
 #### Breaking Changes

auditlog/models.py

@@ -25,6 +25,8 @@
 
 from auditlog.diff import mask_str
 
+DEFAULT_OBJECT_REPR = "<error forming object repr>"
+
 
 class LogEntryManager(models.Manager):
     """
@@ -54,7 +56,11 @@ def log_create(self, instance, force_log: bool = False, **kwargs):
                 "content_type", ContentType.objects.get_for_model(instance)
             )
             kwargs.setdefault("object_pk", pk)
-            kwargs.setdefault("object_repr", smart_str(instance))
+            try:
+                object_repr = smart_str(instance)
+            except ObjectDoesNotExist:
+                object_repr = DEFAULT_OBJECT_REPR
+            kwargs.setdefault("object_repr", object_repr)
             kwargs.setdefault(
                 "serialized_data", self._get_serialized_data_or_none(instance)
             )
@@ -96,7 +102,11 @@ def log_m2m_changes(
                 "content_type", ContentType.objects.get_for_model(instance)
             )
             kwargs.setdefault("object_pk", pk)
-            kwargs.setdefault("object_repr", smart_str(instance))
+            try:
+                object_repr = smart_str(instance)
+            except ObjectDoesNotExist:
+                object_repr = DEFAULT_OBJECT_REPR
+            kwargs.setdefault("object_repr", object_repr)
             kwargs.setdefault("action", LogEntry.Action.UPDATE)
 
             if isinstance(pk, int):

auditlog_tests/models.py

@@ -86,6 +86,9 @@ class RelatedModel(RelatedModelParent):
 
     history = AuditlogHistoryField(delete_related=True)
 
+    def __str__(self):
+        return f"RelatedModel #{self.pk} -> {self.related.id}"
+
 
 class ManyRelatedModel(models.Model):
     """

auditlog_tests/tests.py

@@ -29,7 +29,7 @@
 from auditlog.context import disable_auditlog, set_actor
 from auditlog.diff import model_instance_diff
 from auditlog.middleware import AuditlogMiddleware
-from auditlog.models import LogEntry
+from auditlog.models import DEFAULT_OBJECT_REPR, LogEntry
 from auditlog.registry import AuditlogModelRegistry, AuditLogRegistrationError, auditlog
 from auditlog.signals import post_log, pre_log
 from auditlog_tests.fixtures.custom_get_cid import get_cid as custom_get_cid
@@ -436,6 +436,15 @@ def test_adding_existing_related_obj(self):
         latest_log_entry = self.obj.history.first()
         self.assertEqual(log_entry.id, latest_log_entry.id)
 
+    def test_object_repr_related_deleted(self):
+        """No error is raised when __str__() raises ObjectDoesNotExist."""
+        # monkey-patching to avoid extra logic in the model
+        with mock.patch.object(self.obj.__class__, "__str__") as mock_str:
+            mock_str.side_effect = self.related.DoesNotExist("I am fake")
+            self.obj.related.add(self.related)
+            log_entry = self.obj.history.first()
+            self.assertEqual(log_entry.object_repr, DEFAULT_OBJECT_REPR)
+
 
 class MiddlewareTest(TestCase):
     """
@@ -1860,6 +1869,25 @@ def test_diff_models_with_related_fields(self):
         model_instance_diff(simple2, simple1)
         model_instance_diff(simple1, simple2)
 
+    def test_object_repr_related_deleted(self):
+        """No error is raised when __str__() loads a related object that has been deleted."""
+        simple = SimpleModel()
+        simple.save()
+        related = RelatedModel(related=simple, one_to_one=simple)
+        related.save()
+        related_id = related.id
+
+        related.refresh_from_db()
+        simple.delete()
+        related.delete()
+
+        log_entry = (
+            LogEntry.objects.get_for_model(RelatedModel)
+            .filter(object_id=related_id)
+            .get(action=LogEntry.Action.DELETE)
+        )
+        self.assertEqual(log_entry.object_repr, DEFAULT_OBJECT_REPR)
+
     def test_when_field_doesnt_exist(self):
         """No error is raised and the default is returned."""
         first = SimpleModel(boolean=True)