#35587: Add QuerySet.partition(*args, **kwargs)
-------------------------------------+-------------------------------------
Reporter: micahcantor | Type: New
| feature
Status: new | Component: Database
| layer (models, ORM)
Version: 5.0 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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A common task with a Django model is to partition the model instances into
two sets, ones that is selected by some filters, and ones that are not.
Naively, the following utility script can accomplish this with
QuerySet.filter() and QuerySet.exclude()
{{{
from django.db.models import QuerySet
from django.db.models.manager import BaseManager
def partition(self, *args, **kwargs):
filtered = self.filter(*args, **kwargs)
excluded = self.exclude(*args, **kwargs)
return filtered, excluded
QuerySet.partition = partition
BaseManager.partition = partition
}}}
For instance, if we have a Book model, we can divide it into those that
are fiction and nonfiction.
{{{
fiction, nonfiction = Book.objects.partition(genre="fiction")
}}}
Obtaining two separate QuerySets is often helpful if we want add further
filters, ordering, or prefetches to one set but not the other.
Adding this method to Django would be a helpful utility, and could also be
implemented more efficiently than my own naive implementation. It would be
difficult for me to suggest a better implementation without a deeper
understanding of the implementations of filter() and exclude().
--
Ticket URL: <https://code.djangoproject.com/ticket/35587>
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