Django 5 update_or_create reverse one to one field

Question

On Django 4.x

Code is working as expected

from django.db import models

class Project(models.Model):
    rough_data = models.OneToOneField(
        "Data",
        related_name="rough_project",
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
    )
    final_data = models.OneToOneField(
        "Data",
        related_name="final_project",
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
    )


class Data(models.Model):
    pass

data, created = Data.objects.update_or_create(
            rough_project=project, defaults=data
        )    

On Django 5.x:

ValueError: The following fields do not exist in this model: rough_project

I do not see any changes related to this in changelog

In Django 4.2 and below it worked as one line with update_or_create and in 5.0 it stopped working, so instead I need to do something like this:

data = getattr(project, "rough_data", None)
if data:
   # update fields here
else:
   # create Data object

Answer 1

In Django 4.x, it did not raise an exception but also did not save the relationship if the object was created — so it was actually not working as expected.

• Django ticket: https://code.djangoproject.com/ticket/34586
• Django PR that fixed¹ it to raise exception: https://github.com/django/django/pull/17112/files

It appears to work as expected only if project.save() is called afterwards.

¹You could fix it to proactively save the relationship instead, by subclassing QuerySet and overriding the create method, and then specifying Data objects to use your Manager:

class CreateSaveReverseOneToOneFieldsQuerySet(models.QuerySet):
    def create(self, **kwargs):
        """
        Create a new object with the given kwargs, saving it to the database and returning the created object.
        Also save objects in reverse OneToOne fields — see https://stackoverflow.com/questions/78863608/django-5-update-or-create-reverse-one-to-one-field.
        """
        obj = self.model(**kwargs)
        self._for_write = True
        obj.save(force_insert=True, using=self.db)

        # Save reverse OneToOne fields
        reverse_one_to_one_fields = frozenset(kwargs).intersection(self.model._meta._reverse_one_to_one_field_names)
        for field_name in reverse_one_to_one_fields:
            getattr(obj, field_name).save()

        return obj


class DataManager(models.manager.BaseManager.from_queryset(CreateSaveReverseOneToOneFieldsQuerySet)):
    pass


class Data(models.Model):
    objects = DataManager()