#19184: Remove EmptyQuerySet
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Reporter: akaariai | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: 1.4
Component: Database | Keywords:
layer (models, ORM) | Has patch: 1
Severity: Normal | Needs tests: 0
Triage Stage: Design | Easy pickings: 0
decision needed |
Needs documentation: 0 |
Patch needs improvement: 1 |
UI/UX: 0 |
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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].
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Ticket URL: <https://code.djangoproject.com/ticket/19184>
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