#26172: Don't query the database when filtering an already empty queryset
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Reporter: seddonym | Owner: nobody
Type: Cleanup/optimization | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords: orm, queryset
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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If you have a queryset that has already been evaluated as empty, and you
filter (or exclude) it, Django will hit the database again, even though
the result will always be an empty queryset.
{{{
>>> queryset = MyModel.objects.filter(my_field='foo')
>>> bool(queryset)
# Hits the database - running bool will cache it
False
>>> queryset
[]
>>> queryset.filter(another_field='bar')
# Hits the database
[]
>>> queryset.exclude(another_field='bar')
# Hits the database
[]
}}}
The ORM should check to see if the queryset is empty before running any
further filters / excludes pointlessly.
--
Ticket URL: <https://code.djangoproject.com/ticket/26172>
Django <https://code.djangoproject.com/>
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