weird header stuff

history_tracking/mixins.py

@@ -2,6 +2,17 @@
 
 
 class HistoricalChangeMixin:
+    @property
+    def prev_record(self):
+        """Get the previous record for this instance"""
+        try:
+            return type(self).objects.filter(
+                history_date__lt=self.history_date,
+                id=self.id
+            ).order_by('-history_date').first()
+        except (AttributeError, TypeError):
+            return None
+
     @property
     def diff_against_previous(self):
         prev_record = self.prev_record
@@ -15,9 +26,14 @@ class HistoricalChangeMixin:
                 "history_id",
                 "history_type",
                 "history_user_id",
+                "history_change_reason",
+                "history_type",
             ] and not field.startswith("_"):
-                old_value = getattr(prev_record, field)
-                new_value = getattr(self, field)
-                if old_value != new_value:
-                    changes[field] = {"old": old_value, "new": new_value}
+                try:
+                    old_value = getattr(prev_record, field)
+                    new_value = getattr(self, field)
+                    if old_value != new_value:
+                        changes[field] = {"old": old_value, "new": new_value}
+                except AttributeError:
+                    continue
         return changes