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
35309	Elide ordering of prefetch querysets for single valued relationships	Laurent Lyaudet	nobody	"While the ordering of multi-valued relationships must be preserved when prefetching relationships is it unnecessary when using `prefetch_related` against single valued relationships.

For example, given the following models

{{{#!python
class Author(models.Model):
    name = models.CharField(max_length=200)

    class Meta:
        ordering = [""name""]


class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, related_name=""books"", on_delete=models.CASCADE)

    class Meta:
        ordering = [""title""]
}}}

The ordering of an author's books in `Author.objects.prefetch_related(""books"")` has a significance as multiple books might be associated with each authors.

It's not the case for a book's author in `Book.objects.prefetch_related(""author"")` through as the relationship can only contain a single author and there is a single way to order the members of a singleton.

In other words `sorted([element], key=sort_func)` will result in `[element]` for any `sort_func`.

This property holds true for all the single valued relationships that the ORM supports (backward and forward 1:1 and forward 1:M) which allows the prefetching to elide any predefined ordering safely to avoid an unnecessary and possibly expensive ordering defined for the related model queryset."	Cleanup/optimization	new	Database layer (models, ORM)	5.0	Normal		prefetch single-valued order_by	Laurent Lyaudet Simon Charette	Accepted	1	0	0	1	0	0