#26690: Add the option in the prefetch_related to have the prefetched results
returned as a list or as a queryset
-------------------------------------+-------------------------------------
Reporter: Ursidours | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: Prefetch | Triage Stage:
prefetch_related queryset | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by charettes):
Personally I'm -0 on adding such a feature for the following reasons:
> In many cases, there is no need to chain further queries to the default
prefetch_related. By explicitly asking for a list it would then become
possible to benefit from the speed improvement.
The default `prefetch_related()` results are stored in a `QuerySet()` in
order to make sure the returned instances' prefetched relations still
behave the same as if they were not prefetched. Storing lists in there
would make such instances/querysets unusable by many components of Django
such as forms and model level validation where it would fail in non-
obvious ways.
Using `Prefetch('relation', to_attr='relation_as_list')` already serves
this purpose and don't think introducing another way to do it such as
`Prefetch('relation', as_list=True)` is worth it. If we'd really want to
speed up default prefetches I think we should investigate assigning
objects that quack like `QuerySet` (e.g. `PrefetchedQuerySet`) but only
lazily build their underlying query when required as this is the part that
slow down performance here.
> Conversely, some developers may be happy to take the performance hit in
order to further refine a Prefetch with to_attr.
I've never personally required to refine a prefetched result, that sounds
like an anti-pattern to me.
--
Ticket URL: <https://code.djangoproject.com/ticket/26690#comment:2>
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