#19195: Using distinct([*fields]) filter on a foreign key produces an ordering
error when the foreign key has a Meta ordering field.
-------------------------------------+-------------------------------------
Reporter: chrisedgemon@… | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.4
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: distinct, query | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by charettes):
* cc: charettes (added)
Old description:
> I tried to using a distinct filter like this:
> Appearance.objects.order_by('team').distinct('team'); this fails with the
> following Database Error: "DatabaseError: SELECT DISTINCT ON expressions
> must match initial ORDER BY expressions"
>
> It is possible to work around this problem by using this modified filter:
> Appearance.objects.order_by('team__id').distinct('team__id').
>
> Model definition: http://pastebin.com/index/J45fy9fr
> Full traceback: http://pastebin.com/feSFMbzX
New description:
I tried to using a distinct filter like this:
Appearance.objects.order_by('team').distinct('team'); this fails with the
following Database Error: "DatabaseError: SELECT DISTINCT ON expressions
must match initial ORDER BY expressions"
It is possible to work around this problem by using this modified filter:
`Appearance.objects.order_by('team__id').distinct('team__id')`.
Model definition: http://pastebin.com/index/J45fy9fr
Full traceback: http://pastebin.com/feSFMbzX
--
Comment:
Just hit this issue and had a hard time figuring out what I've done wrong.
Intuitively I tried `.distinct('related_id').order_by('related_id')` after
realizing removing my `Related._meta.ordering` solved the issue but, as
pointed out by akaariai, this is not allowed ATM.
Replying to [comment:3 akaariai]:
> I think we should allow using .order_by('team_id') here.
>
> Related fields have two attributes on model level - team and team_id in
this case. We allow using team_id in many places in the ORM already, and
to me it seems we should allow it in order_by and distinct, too.
>
> Is there some reason to *not* allow them?
I can't think of any reason we'd like *not* to allow them. It looks like
sanest to expose an API to explicitly opt-out of the existing related
model ordering behavior while maintaining backward compatibility.
--
Ticket URL: <https://code.djangoproject.com/ticket/19195#comment:6>
Django <https://code.djangoproject.com/>
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