#35356: Issue with OneToOneField and recursive relationships in select_related()
and only().
-------------------------------------+-------------------------------------
Reporter: Joshua | Owner: nobody
van Besouw |
Type: Bug | Status: new
Component: Database | Version: 4.2
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
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.
--
Ticket URL: <https://code.djangoproject.com/ticket/35356>
Django <https://code.djangoproject.com/>
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