id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
35356	Issue with OneToOneField and recursive relationships in select_related() and only().	Joshua van Besouw	Simon Charette	"In Django a 4.2 project, if you have a model with a recursive relationship `OneToOneField` like this:

{{{
class Example(models.Model):
    name = models.CharField(max_length=32)
    source = models.OneToOneField(
        'self', related_name='destination', on_delete=models.CASCADE
    )
}}}

And then query this model using:

{{{
Example.objects.select_related(
    ""source"",
    ""destination"",
).only(
    ""name"",
    ""source__name"",
    ""destination__name"",
).all()
}}}

It throws the following error:

{{{
django.core.exceptions.FieldError: Field Example.source cannot be both deferred and traversed using select_related at the same time.
}}}

**Expected behavior:**

The queryset should apply the `select_related()` and `only()` without an exception occurring as the `only()` is specifying sub fields of the fields in the `select_related()`. Or at least this is how it used to behave.

Interestingly, if you change the queryset to the following, it works without any issues:

{{{
Example.objects.select_related(""source"").only(""name"", ""source__name"").all()
}}}

And vice versa also works:

{{{
Example.objects.select_related(""destination"").only(""name"", ""destination__name"").all()
}}}

**Effected versions:**

This error occurs in version 4.2+ of Django.

This worked as expected in all versions of Django 4.1. 

As far as I can tell, this is a regression as a brief search doesn't indicate this functionality was explicitly changed at any point. I have not tested whether this is only an issue with recursive relationships or a general issues with reverse relationships."	Bug	closed	Database layer (models, ORM)	4.2	Normal	fixed		Joshua van Besouw	Ready for checkin	1	0	0	0	0	0