Resolve "'FieldInstanceTracker' object has no attribute 'saved_data'"

Closes #639 (closed)

aleksis/core/migrations/0035_preference_model_unique.py

@@ -12,11 +12,7 @@ class Migration(migrations.Migration):
     ]
 
     def _migrate_preference_models_to_unique(apps, schema_editor):
-        GroupPreferenceModel = apps.get_model("core", "GroupPreferenceModel")
-        PersonPreferenceModel = apps.get_model("core", "PersonPreferenceModel")
-        SitePreferenceModel = apps.get_model("core", "SitePreferenceModel")
-
-        from dynamic_preferences.models import BasePreferenceModel
+        from aleksis.core.models import GroupPreferenceModel, PersonPreferenceModel, SitePreferenceModel
 
         models = [GroupPreferenceModel, PersonPreferenceModel, SitePreferenceModel]
 
@@ -32,7 +28,7 @@ class Migration(migrations.Migration):
                 if len(objs) > 1:
                     found = False
                     for obj in objs:
-                        if BasePreferenceModel.get_value(obj) == BasePreferenceModel.preference(obj).default or found:
+                        if obj.value == obj.preference.default or found:
                             obj.delete()
                         else:
                             found = True