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
7214	Bug in OneToOneField cache	m.gajda@…	nobody	"There is a fatal bug in OneToOneField cacheing subsystem. Consider following models:

{{{
class A( models.Model ):
  foo = models.IntegerField()

  def __unicode__( self ):
    return ""%d"" % self.foo

class B( A ):
    a = models.OneToOneField( A , related_name = ""b"" , parent_link = True )

class C( A ):
    a = models.OneToOneField( A , related_name = ""c"" , parent_link = True )

> B(foo=1).save()

> C(foo=2).save()

> A.objects.all()
[<A: 1>, <A: 2>]

> a = A.objects.filter( foo = 1 )[0]

> a.b
<B: 1>

> a.c
<B: 1>
}}}

In both cases (''b'' and ''c'' fields pointing to different subclasses) is returns the same object, but in the second case an exception should be throwed.

The reason is cacheing subsystem in ''SingleRelatedObjectDescriptor'' class of the module ''django.db.models.fields.related''. In the constructor it creates twice cache with the same so called cache name: ''self.cache_name = '_%s_cache' % related.field.name'' because ''related.field.name'' points to the same string in both cases. In my opinion it should point to different strings. After aplying attached patch, which uses just ''related.name'' instead of ''related.field.name'' everything seems to work correctly (cache still works but separately for both fields).

{{{
> A.objects.all()
[<A: 1>, <A: 2>]

> a = A.objects.filter( foo = 1 )[0]

> a.b
<B: 1>

> a.c
<class 'megasite.test.models.DoesNotExist'>: C matching query does not exist.
}}}
"		closed	Core (Other)	dev		duplicate	one to one cache bug		Unreviewed	1	0	0	0	0	0