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
19184	Remove EmptyQuerySet	Anssi Kääriäinen	nobody	"qs.none() is currently implemented by returning an !EmptyQuerySet which has no-op operators for most of the !QuerySet methods.

This approach has several weaknesses:
  - Doesn't work well with subclasses of !QuerySet (#17271)
  - Doesn't work well when Django uses subclasses internally to implement some functionality (values() for example, #15959)
  - The EmptyQS doesn't actually work like !QuerySet - for example qs.none().filter(nonexisting_field=someval). Also: #19173.
  - Code duplication: the EmptyQS has around 150 lines of code duplicating the methods of QS. The duplicated methods just do return self. If you add a method to QS and forget it from EmptyQS strange things can happen.

Problems if removing EmptyQS:
  - We have documented it in [https://docs.djangoproject.com/en/dev/ref/models/querysets/#django.db.models.query.QuerySet.none qs.none()] docs. And, I can't see any way to have a deprecation period for this.
  - There will be some performance penalty mainly from queryset cloning as the qs.none() methods now actually do something.

I am obviously +1 to just removing the !EmptyQS. The question is if people are relying on isinstance(someqs, !EmptyQuerySet) calls in their code. If so, we could add ""known_empty"" property so that users could check if it is possible for this queryset to return any values.

A work-in-progress patch available from [https://github.com/akaariai/django/compare/rm_emptyqs branch akaariai/django/rm_emptyqs]."	Cleanup/optimization	closed	Database layer (models, ORM)	1.4	Normal	fixed			Ready for checkin	1	0	0	0	0	0