add add_current_model and get_field_value to utils.py

src/c3nav/editor/models/changeset.py

@@ -11,7 +11,7 @@ from django.utils.translation import ugettext_lazy as _
 from django.utils.translation import ungettext_lazy
 
 from c3nav.editor.models.change import Change
-from c3nav.editor.utils import is_created_pk
+from c3nav.editor.utils import get_current_obj, get_field_value, is_created_pk
 from c3nav.editor.wrappers import ModelInstanceWrapper, ModelWrapper
 from c3nav.mapdata.models import LocationSlug
 from c3nav.mapdata.models.locations import LocationRedirect
@@ -381,10 +381,8 @@ class ChangeSet(models.Model):
         model = type(obj)
         field = model._meta.get_field('titles' if name.startswith('title_') else name)
         with transaction.atomic():
-            if is_created_pk(obj.pk):
-                current_obj = model()
-            else:
-                current_obj = model.objects.only(field.name).get(pk=obj.pk)
+            current_obj = get_current_obj(model, obj.pk)
+            current_value = get_field_value(current_obj, field)
             try:
                 current_value = getattr(current_obj, field.attname)
             except AttributeError:

src/c3nav/editor/utils.py

@@ -1,2 +1,31 @@
+from typing import Union
+
+from django.db import models
+
+
 def is_created_pk(pk):
     return isinstance(pk, str) and pk.startswith('c') and pk[1:].isnumeric()
+
+
+def get_current_obj(model, pk, only_field=None):
+    if is_created_pk(pk):
+        return model()
+    if only_field is not None:
+        return model.objects.only(only_field).get(pk=pk)
+    return model.objects.get(pk=pk)
+
+
+def get_field_value(obj, field: Union[str, models.Field]):
+    if isinstance(field, str):
+        name = field
+        model = type(obj)
+        field = model._meta.get_field('titles' if name.startswith('title_') else name)
+    else:
+        name = field.name
+    try:
+        current_value = getattr(obj, field.attname)
+    except AttributeError:
+        current_value = field.to_prep_value(getattr(obj, field.name))
+    if name.startswith('title_'):
+        current_value = current_value.get(name[6:], '')
+    return current_value