Audit changes to FK fields when saved using *_id naming. (#525)

* Audit changes to FK fields when saved using *_id naming.

In Django you can save changes to a FK field on a model using the ID
field name (attname) in addition to the regular FK field name with:

    model.related_model_id = 42
    model.save(update_fields=["related_model_id'])

or:

    model.related_model = related_model
    model.save(update_fields=["related_model_id'])

as opposed to the more common:

    model.related_model = related_model
    model.save(update_fields=["related_model'])

This change ensures those model changes are logged properly.

* Apply suggested change from code review.

* Add a CHANGELOG entry for the fix.

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 #### Fixes
 
+- fix: Audit changes to FK fields when saved using `*_id` naming. ([#525](https://github.com/jazzband/django-auditlog/pull/525))
 - fix: Fix a bug in audit log admin page when `USE_TZ=False`. ([#511](https://github.com/jazzband/django-auditlog/pull/511))
 - fix: Make sure `LogEntry.changes_dict()` returns an empty dict instead of `None` when `json.loads()` returns `None`. ([#472](https://github.com/jazzband/django-auditlog/pull/472))
 - fix: Always set remote_addr even if the request has no authenticated user. ([#484](https://github.com/jazzband/django-auditlog/pull/484))

auditlog/diff.py

@@ -4,7 +4,7 @@ from typing import Optional
 
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
-from django.db.models import NOT_PROVIDED, DateTimeField, JSONField, Model
+from django.db.models import NOT_PROVIDED, DateTimeField, ForeignKey, JSONField, Model
 from django.utils import timezone as django_timezone
 from django.utils.encoding import smart_str
 
@@ -147,7 +147,14 @@ def model_instance_diff(
         model_fields = None
 
     if fields_to_check:
-        fields = {field for field in fields if field.name in fields_to_check}
+        fields = {
+            field
+            for field in fields
+            if (
+                (isinstance(field, ForeignKey) and field.attname in fields_to_check)
+                or (field.name in fields_to_check)
+            )
+        }
 
     # Check if fields must be filtered
     if (

auditlog_tests/tests.py

@@ -1858,6 +1858,32 @@ class TestRelatedDiffs(TestCase):
         self.assertEqual(int(log_one.changes_dict["one_to_one"][1]), simple.id)
         self.assertEqual(int(log_two.changes_dict["related"][1]), two_simple.id)
 
+    def test_log_entry_changes_on_fk_object_id_update(self):
+        t1 = self.test_date
+        with freezegun.freeze_time(t1):
+            simple = SimpleModel.objects.create()
+            one_simple = SimpleModel.objects.create()
+            two_simple = SimpleModel.objects.create()
+            instance = RelatedModel.objects.create(
+                one_to_one=simple, related=one_simple
+            )
+
+        t2 = self.test_date + datetime.timedelta(days=20)
+        with freezegun.freeze_time(t2):
+            instance.related_id = two_simple.id
+            instance.one_to_one = one_simple
+            instance.save(update_fields=["related_id", "one_to_one_id"])
+
+        log_one = instance.history.filter(timestamp=t1).first()
+        log_two = instance.history.filter(timestamp=t2).first()
+        self.assertTrue(isinstance(log_one, LogEntry))
+        self.assertTrue(isinstance(log_two, LogEntry))
+
+        self.assertEqual(int(log_one.changes_dict["related"][1]), one_simple.id)
+        self.assertEqual(int(log_one.changes_dict["one_to_one"][1]), simple.id)
+        self.assertEqual(int(log_two.changes_dict["related"][1]), two_simple.id)
+        self.assertEqual(int(log_two.changes_dict["one_to_one"][1]), one_simple.id)
+
     def test_log_entry_changes_on_fk_id_update(self):
         t1 = self.test_date
         with freezegun.freeze_time(t1):