#35587: Add QuerySet.partition(*args, **kwargs)
-------------------------------------+-------------------------------------
Reporter: Micah Cantor | Owner: (none)
Type: New feature | Status: closed
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution: wontfix
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Simon Charette):
* resolution: => wontfix
* status: new => closed
Comment:
I don't think it's worth extending the `Queryset` API with a method that
can be emulated through various method and would entertain the idea that
the returned set of objects will always be mutually exclusive. This is not
a guarantee that the ORM can provide for a few reasons.
First the querysets are going to reach to the database serially and thus
they won't be executed against the same ''snapshot'' so an object could be
changed in a way that makes it appear in both partitions. Secondly, while
the ORM goes at great length to make `exclude` the complement of `filter`
[https://code.djangoproject.com/query?description=~exclude&status=assigned&status=new&order=id&desc=1
it has a few know bugs] which could also manifest themselves in these
scenarios.
You are likely better off with a single query that uses an annotation as
the Python-level predicate for partitioning
{{{#!python
def partition(self, *args, **kwargs):
queryset = self.annotate(_partition_predicate=Q(*args, **kwargs))
predicate = attrgetter("_partition_predicate")
return filter(predicate, queryset), filterfalse(predicate, queryset)
}}}
But that doesn't allow chaining which for the aforementioned reasons I
believe is not achievable.
--
Ticket URL: <https://code.djangoproject.com/ticket/35587#comment:1>
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