#24762: Proxy models with children which inherit from the proxy cannot
select_related said children
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Reporter: kezabelle | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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This has only been briefly checked on `1.7`, `1.8` and
`django-1.9.dev20150506223347` (`master`), and appears to silently pass on
1.6 (because `select_related` previously didn't raise errors)
Given the following models:
{{{
class InheritanceProxyConcrete(models.Model):
pass
class InheritanceProxy(InheritanceProxyConcrete):
class Meta:
proxy = True
class InheritanceProxyChild(InheritanceProxy):
pass
}}}
I would expect to be able to do the following:
{{{
>>> InheritanceProxy.objects.select_related('inheritanceproxychild')
[<InheritanceProxy: InheritanceProxy object>]
# equating to something like
SELECT "tests_inheritanceproxyconcrete"."id",
"tests_inheritanceproxychild"."inheritanceproxyconcrete_ptr_id" FROM
"tests_inheritanceproxyconcrete" LEFT OUTER JOIN
"tests_inheritanceproxychild" ON ( "tests_inheritanceproxyconcrete"."id" =
"tests_inheritanceproxychild"."inheritanceproxyconcrete_ptr_id" )
}}}
however, it transpires that it doesn't work:
{{{
>>>
InheritanceProxyConcrete.objects.select_related('inheritanceproxychild')
[<InheritanceProxyConcrete: InheritanceProxyConcrete object>]
>>> InheritanceProxy.objects.select_related('inheritanceproxychild')
FieldError: Invalid field name(s) given in select_related:
'inheritanceproxychild'. Choices are: (none)
>>> InheritanceProxy.objects.select_related('inheritanceproxychild_ptr')
FieldError: Invalid field name(s) given in select_related:
'inheritanceproxychild_ptr'. Choices are: (none)
}}}
Furthering the quirkiness of the problem:
{{{
>>> dir(InheritanceProxy)
['DoesNotExist', 'MultipleObjectsReturned', '__class__', ...
'inheritanceproxychild', ...]
>>> InheritanceProxy.inheritanceproxychild
<django.db.models.fields.related.SingleRelatedObjectDescriptor object at
0xBLAHBlAH>
}}}
I've not worked with proxies much, and certainly not recently, so there's
a good probability I'm making assumptions about what functionality should
be provided based on an incomplete understanding of their use cases.
I've not tested explicit `OneToOnes`, `ForeignKeys`, `ManyToManys` or
`prefetch_related`, so the possibility remains that it is only implicit
parentage `OneToOnes` which are affected.
This stems from a ticket downstream in [https://github.com/carljm/django-
model-utils/issues/168 django-model-utils] regarding using a Proxy model
as the parent for auto-downcasting model instances (using it's
`InheritanceManager`)
--
Ticket URL: <https://code.djangoproject.com/ticket/24762>
Django <https://code.djangoproject.com/>
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