Track changed fields in activity to model code

bookwyrm/activitypub/base_activity.py

@@ -106,6 +106,7 @@ class ActivityObject:
                 value = field.default
             setattr(self, field.name, value)
 
+    # pylint: disable=too-many-locals,too-many-branches
     def to_model(self, model=None, instance=None, allow_create=True, save=True):
         """convert from an activity to a model instance"""
         model = model or get_model_from_type(self.type)
@@ -126,27 +127,36 @@ class ActivityObject:
             return None
         instance = instance or model()
 
+        # keep track of what we've changed
+        update_fields = []
         for field in instance.simple_fields:
             try:
-                field.set_field_from_activity(instance, self)
+                changed = field.set_field_from_activity(instance, self)
+                if changed:
+                    update_fields.append(field.name)
             except AttributeError as e:
                 raise ActivitySerializerError(e)
 
         # image fields have to be set after other fields because they can save
         # too early and jank up users
         for field in instance.image_fields:
-            field.set_field_from_activity(instance, self, save=save)
+            changed = field.set_field_from_activity(instance, self, save=save)
+            if changed:
+                update_fields.append(field.name)
 
         if not save:
             return instance
 
         with transaction.atomic():
+            # can't force an update on fields unless the object already exists in the db
+            if not instance.id:
+                update_fields = None
             # we can't set many to many and reverse fields on an unsaved object
             try:
                 try:
-                    instance.save(broadcast=False)
+                    instance.save(broadcast=False, update_fields=update_fields)
                 except TypeError:
-                    instance.save()
+                    instance.save(update_fields=update_fields)
             except IntegrityError as e:
                 raise ActivitySerializerError(e)