bulk_create of parent after setting on child leads to unexpected data loss

[Hannes Ljungberg]

I think this is a missed case of https://code.djangoproject.com/ticket/28147. The behaviour is exactly the same but affects bulk_update.

Failing testcase:

parent = NoFields()
child = NullableFields(auto_field=parent)
NoFields.objects.bulk_create([parent])
NullableFields.objects.bulk_create([child])
child.refresh_from_db()
self.assertEqual(child.auto_field, parent)

This behaviour was also described in https://code.djangoproject.com/ticket/29497 but might’ve been missed when closed as a duplicate.

My proposal is to extract the code in Model.save() which ensures that all fields are in sync before save to it’s own method which can then be used by bulk_update.

[Hannes Ljungberg]

PR: ​https://github.com/django/django/pull/13589

[Mariusz Felisiak]

Thanks, let's reopen the original report.

Duplicate of #29497.