#35317: Add the possibility to do prefetches for only a subset of instances
-------------------------------------+-------------------------------------
Reporter: Laurent Lyaudet | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Simon Charette):
I'm not convinced we should add a feature for that given
`prefetch_related_objects` is already
[https://docs.djangoproject.com/en/5.0/ref/models/querysets/#django.db.models.prefetch_related_objects
a documented public API] that allows for this feature to be built on top
of
{{{#!python
orders = (
Order.objects.filter(...)
.exclude(...)
.annotate(...)
.prefetch_related(
"items",
"address",
)
)
predicate = lambda packing_task:
order.needs_to_consider_packing_problematic_zonings()
problematic_orders = filter(predicate, orders)
prefetch_related_objects(
orders,
Prefetch(
"packing_task__zonings",
queryset=Zonings.objects.filter(...),
to="problematic_zonings"
),
)
}}}
I'd a bit more trickier when dealing with predicates for nested prefetches
but it's still doable.
Just like any other non-trivial feature addition like this one I suggest
trying to gather consensus on a general need for
[https://docs.djangoproject.com/en/5.0/internals/contributing/bugs-and-
features/#requesting-features this feature] on the forum and / or
developer mailing list. From providing support over this channels in the
past years I don't remember anyone else running into a similar issue that
couldn't be solved with `prefetch_related_objects` directly.
--
Ticket URL: <https://code.djangoproject.com/ticket/35317#comment:4>
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