#15807: order by 'pk' alias doesn't work with inherited models when parent has
an
ordering set
-------------------------------------+-------------------------------------
Reporter: mat | Owner: nobody
Type: Bug | Status: closed
Milestone: | Component: Database layer
Version: SVN | (models, ORM)
Resolution: wontfix | Severity: Normal
Triage Stage: | Keywords:
Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
-------------------------------------+-------------------------------------
Changes (by jacob):
* status: new => closed
* resolution: => wontfix
* easy: => 0
Comment:
So here's why this is happening:
`pk` is translated to "the name of the primary key column". `Child`, as a
concrete subclass, has a primary key that has a foreign key (technically a
`OneToOneField` with `parent_link=True`) to `Foo`. In other words, your
models, with the field implicitly added by the subclassing, ''actually''
are like:
{{{
#!python
class Foo(models.Model):
bar = models.PositiveSmallIntegerField(default=1)
class Child(models.Model):
foo_ptr = models.OneToOneField(Foo, parent_link=True)
barchild = models.PositiveSmallIntegerField(default=1)
}}}
This means that `Child.objects.order_by("pk")` actually translates to
`Child.objects.order_by("foo_ptr")`. Remember, `foo_ptr` is a foreign key
(one-to-one fields are just a special kind of foreign key). This is
important, because `order_by("some_foreign_key")` translates to "order by
the default ordering for the object pointed to by the foreign key". As
[http://docs.djangoproject.com/en/dev/ref/models/querysets/#order-by the
documentation says]:
If you try to order by a field that is a relation to another model,
Django will use the default ordering on the related model (or order by the
related model's primary key if there is no Meta.ordering specified.
The object pointed to, in this case, is `Foo`. So
`Child.objects.order_by("pk")` is in fact working correctly, if a bit
counterintuitively.
We ''could'' change this, but it would introduce other subtle
counterintuitive problems and would quite likely be backwards-
incompatible. So I'm going to mark this wontfix. I know it's not ideal,
but I'm afraid the cure is worse than the disease here.
--
Ticket URL: <http://code.djangoproject.com/ticket/15807#comment:2>
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