#34889: Broken fallback for prefetchers that only implement
get_prefetch_queryset
-------------------------------------+-------------------------------------
Reporter: Matt | Owner: nobody
Westcott |
Type: Bug | Status: new
Component: Database | Version: 5.0
layer (models, ORM) |
Severity: Release | Keywords:
blocker |
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
In #33651, the `get_prefetch_queryset()` method of related managers and
descriptors is deprecated in favour of `get_prefetch_querysets()`. Based
on the deprecation warnings, it's clear that subclasses implementing only
`get_prefetch_queryset()` are intended to continue working until this is
removed outright in 6.0. However, the fallback code in
`prefetch_one_level` calls it with an invalid signature:
https://github.com/django/django/blob/4e790271e3e65c9ad037b347a34fa95e11982228/django/db/models/query.py#L2535-L2562
Here the `get_prefetch_queryset` method is passed
`lookup.get_current_querysets(level)` - which returns a list of querysets
- as the `queryset` argument, which expects a single queryset. Changing
this to `lookup.get_current_queryset(level)` fixes the problem (although
it also doubles up the deprecation warnings, which may not be ideal).
Unfortunately I'm slightly stumped over how I might create a regression
test for this - presumably this would involve writing a minimal related
manager class that implements `get_current_queryset` but not
`get_current_querysets`, but since this is an internal API it's hard to
know what's considered minimal while still being a legal implementation.
If it's any help, I encountered this as a regression to the `django-
modelcluster` package: https://github.com/wagtail/django-
modelcluster/actions/runs/6407673311/job/17394971115
--
Ticket URL: <https://code.djangoproject.com/ticket/34889>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to django-updates+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/0107018afbd0c168-f24cf03a-f618-4f36-9e4b-c8ccce0a6bc5-000000%40eu-central-1.amazonses.com.
