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
26523	Unable to select_related() an implicit one to one relationship in multi-table inheritance	Paulo	nobody	"Given the following models:


{{{
class Fruit(models.Model):
    weight = models.PositiveIntegerField(default=100)


class Apple(Fruit):
    farmer = models.CharField(max_length=200, blank=True)


class Kiwi(models.Model):
    fruit = models.OneToOneField(Fruit)
    farmer = models.CharField(max_length=200, blank=True)
}}}

I would like to prefetch the fruit object related to an apple or kiwi.

So I ran the following:


{{{
In [2]: kiwi = Kiwi.objects.select_related('fruit').latest('id')
QUERY = u'SELECT ""fruits_kiwi"".""id"", ""fruits_kiwi"".""fruit_id"", ""fruits_kiwi"".""farmer"", ""fruits_fruit"".""id"", ""fruits_fruit"".""weight"" FROM ""fruits_kiwi"" INNER JOIN ""fruits_fruit"" ON ( ""fruits_kiwi"".""fruit_id"" = ""fruits_fruit"".""id"" ) ORDER BY ""fruits_kiwi"".""id"" DESC LIMIT 1' - PARAMS = () [0.84ms]

In [3]: kiwi.fruit
Out[3]: <Fruit: Fruit #00021>
}}}

As you can see, calling kiwi.fruit does not result in any extra queries.

Now I tried with Apple:


{{{
In [4]: apple = Apple.objects.select_related('fruit_ptr').latest('id')
QUERY = u'SELECT ""fruits_fruit"".""id"", ""fruits_fruit"".""weight"", ""fruits_apple"".""fruit_ptr_id"", ""fruits_apple"".""farmer"" FROM ""fruits_apple"" INNER JOIN ""fruits_fruit"" ON ( ""fruits_apple"".""fruit_ptr_id"" = ""fruits_fruit"".""id"" ) ORDER BY ""fruits_apple"".""fruit_ptr_id"" DESC LIMIT 1' - PARAMS = () [0.31ms]

In [5]: apple.fruit_ptr
QUERY = u'SELECT ""fruits_fruit"".""id"", ""fruits_fruit"".""weight"" FROM ""fruits_fruit"" WHERE ""fruits_fruit"".""id"" = %s' - PARAMS = (16,) [0.35ms]
Out[5]: <Fruit: Fruit #00016>
}}}

Calling apple.fruit_ptr results in a query to the database even though it's set to prefetch the related fruit.

I've traced the bug to https://github.com/django/django/blob/stable/1.8.x/django/db/models/query_utils.py#L186"	Bug	closed	Database layer (models, ORM)	1.8	Normal	duplicate			Unreviewed	0	0	0	0	0	0