Fix diff_against on model with non-editable fields

Author: dracos

AUTHORS.rst

@@ -82,6 +82,7 @@ Authors
 - Martin Bachwerk
 - Marty Alchin
 - Matheus Cansian (`mscansian <https://github.com/mscansian>`_)
+- Matthew Somerville (`dracos <https://github.com/dracos>`_)
 - Mauricio de Abreu Antunes
 - Maxim Zemskov (`MaximZemskov <https://github.com/MaximZemskov>`_)
 - Micah Denbraver

CHANGES.rst

@@ -28,6 +28,7 @@ Full list of changes:
 - Add Python 3.10 to test matrix (gh-899)
 - Added support for Django 4.0 (gh-898)
 - Dropped support for Python 3.6, which reached end-of-life on 2021-12-23 (gh-946).
+- Fix bug with ``history.diff_against`` with non-editable fields (gh-923)
 
 3.0.0 (2021-04-16)
 ------------------

simple_history/models.py

@@ -646,7 +646,9 @@ def diff_against(self, old_history, excluded_fields=None, included_fields=None):
             excluded_fields = set()
 
         if included_fields is None:
-            included_fields = {f.name for f in old_history.instance_type._meta.fields}
+            included_fields = {
+                f.name for f in old_history.instance_type._meta.fields if f.editable
+            }
 
         fields = set(included_fields).difference(excluded_fields)
 

simple_history/tests/models.py

@@ -25,6 +25,14 @@ def get_absolute_url(self):
         return reverse("poll-detail", kwargs={"pk": self.pk})
 
 
+class PollWithNonEditableField(models.Model):
+    question = models.CharField(max_length=200)
+    pub_date = models.DateTimeField("date published")
+    modified = models.DateTimeField(auto_now=True, editable=False)
+
+    history = HistoricalRecords()
+
+
 class PollWithUniqueQuestion(models.Model):
     question = models.CharField(max_length=200, unique=True)
     pub_date = models.DateTimeField("date published")

simple_history/tests/tests/test_models.py

@@ -78,6 +78,7 @@
     Place,
     Poll,
     PollInfo,
+    PollWithNonEditableField,
     PollWithExcludedFieldsWithDefaults,
     PollWithExcludedFKField,
     PollWithExcludeFields,
@@ -720,6 +721,18 @@ def test_history_diff_with_included_fields(self):
         self.assertEqual(delta.changed_fields, ["question"])
         self.assertEqual(len(delta.changes), 1)
 
+    def test_history_diff_with_non_editable_field(self):
+        p = PollWithNonEditableField.objects.create(
+            question="what's up?", pub_date=today
+        )
+        p.question = "what's up, man?"
+        p.save()
+        new_record, old_record = p.history.all()
+        with self.assertNumQueries(0):
+            delta = new_record.diff_against(old_record)
+        self.assertEqual(delta.changed_fields, ["question"])
+        self.assertEqual(len(delta.changes), 1)
+
     def test_history_with_unknown_field(self):
         p = Poll.objects.create(question="what's up?", pub_date=today)
         p.question = "what's up, man?"