Deferred fields patch (#1393)

* added patch and test

* added myself to AUTHORS

* adde my change to CHANGES.rst

* fixed bug to connect to pre_delete instead of post_delete

* implemented suggestion made by @jwaschkau in issue #1064

* added .python-version to the .gitignore

* -  added check to signal to see if instance is history enabled before loading its deferred fields

* check that fields is "truthy" before calling refresh_from_db

* added to test to ensure by-pass logic is covered

.gitignore

@@ -6,6 +6,7 @@
 .idea
 .tox/
 .venv/
+.python-version
 /.project
 /.pydevproject
 /.ve

CHANGES.rst

@@ -7,6 +7,7 @@ Unreleased
 - Made ``skip_history_when_saving`` work when creating an object - not just when
   updating an object (gh-1262)
 - Improved performance of the ``latest_of_each()`` history manager method (gh-1360)
+- Fixed issue with deferred fields causing DoesNotExist error (gh-678)
 - Added HistoricOneToOneField (gh-1394)
 
 3.7.0 (2024-05-29)

simple_history/models.py

@@ -221,6 +221,7 @@ def finalize(self, sender, **kwargs):
         # so the signal handlers can't use weak references.
         models.signals.post_save.connect(self.post_save, sender=sender, weak=False)
         models.signals.post_delete.connect(self.post_delete, sender=sender, weak=False)
+        models.signals.pre_delete.connect(self.pre_delete, sender=sender, weak=False)
 
         m2m_fields = self.get_m2m_fields_from_model(sender)
 
@@ -668,6 +669,23 @@ def post_delete(self, instance, using=None, **kwargs):
         else:
             self.create_historical_record(instance, "-", using=using)
 
+    def pre_delete(self, instance, **kwargs):
+        """
+        pre_delete method to ensure all deferred fileds are loaded on the model
+        """
+        # First check that history is enabled (on model and globally)
+        if not getattr(settings, "SIMPLE_HISTORY_ENABLED", True):
+            return
+        if not hasattr(instance._meta, "simple_history_manager_attribute"):
+            return
+        fields = self.fields_included(instance)
+        field_attrs = {field.attname for field in fields}
+        deferred_attrs = instance.get_deferred_fields()
+        # Load all deferred fields that are present in fields_included
+        fields = field_attrs.intersection(deferred_attrs)
+        if fields:
+            instance.refresh_from_db(fields=fields)
+
     def get_change_reason_for_object(self, instance, history_type, using):
         """
         Get change reason for object.

simple_history/tests/tests/test_models.py

@@ -945,6 +945,18 @@ def test_history_with_unknown_field(self):
         with self.assertNumQueries(0):
             new_record.diff_against(old_record, excluded_fields=["unknown_field"])
 
+    def test_delete_with_deferred_fields(self):
+        Poll.objects.create(question="what's up bro?", pub_date=today)
+        Poll.objects.create(question="what's up sis?", pub_date=today)
+        Poll.objects.only("id").first().delete()
+        Poll.objects.defer("question").all().delete()
+        # Make sure bypass logic runs
+        Place.objects.create(name="cool place")
+        Place.objects.defer("name").first().delete()
+        with self.settings(SIMPLE_HISTORY_ENABLED=False):
+            Place.objects.create(name="cool place")
+            Place.objects.defer("name").all().delete()
+
     def test_history_with_custom_queryset(self):
         PollWithQuerySetCustomizations.objects.create(
             id=1, pub_date=today, question="Question 1"