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
30894	Reverse OneToOneField relation: `prefetch_related` uses `related_name` while `select_related` uses `related_query_name`	Adam Sołtysik	nobody	"The documentation (https://docs.djangoproject.com/en/2.2/ref/models/querysets/#select-related) states:

  You can also refer to the reverse direction of a OneToOneField in the list of fields passed to select_related — that is, you can traverse a OneToOneField back to the object on which the field is defined. Instead of specifying the field name, use the related_name for the field on the related object.

But in fact `related_query_name` is used by `select_related` and `related_name` is used by `prefetch_related` .

When we have the following models:

{{{
class A(Model):
    pass
}}}
{{{
class B(Model):
    a = OneToOneField('A', related_name='b_set', related_query_name='b')
}}}

then `a.select_related('b')` works and `a.prefetch_related('b')` does not:

{{{AttributeError: Cannot find 'b' on A object, 'b' is an invalid parameter to prefetch_related()}}}

or if class `A` happens to have a property named `b`:

{{{ValueError: 'b' does not resolve to an item that supports prefetching - this is an invalid parameter to prefetch_related().}}}

And vice versa, `a.prefetch_related('b_set')` works and `a.select_related('b_set')` does not:

{{{django.core.exceptions.FieldError: Invalid field name(s) given in select_related: 'b_set'. Choices are: b}}}

The documentation implies that both methods should use `related_name`, but I think it would be more intuitive if both used `related_query_name`, given that we can write lookups like in filter queries etc., and such a change would probably be less backward-incompatible."	Cleanup/optimization	closed	Database layer (models, ORM)	2.2	Normal	wontfix			Unreviewed	0	0	0	0	0	0