#26565: Allow Prefetch query to use .values()
-------------------------------------+-------------------------------------
Reporter: Maxime Lorant | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: prefetch, values | Triage Stage: Accepted
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 Simon Charette):
> What's the workaround for this if I have a similar need?
Perform the prefetch queryset and attribute assignment yourself. In the
end `prefetch_related` only does the following
It transforms
{{{#!python
Authors.objects.filter(popular=True).prefetch_related(Prefetch("books",
to_attr="prefetched_books"))
}}}
Into
{{{#!python
authors = Authors.objects.filter(popular=True)
authors_books = defaultdict(list)
for book in Book.objects.filter(author__in=authors):
authors_books[book.author_id].append(book)
for author in authors:
setattr(author, "prefetched_books", authors_books[author.pk])
}}}
So as long as the back references is included in your `values` (which is
something the `prefetch_related` code would need to do anyway and the part
Micah ran into issues with) you should be able to achieve the same thing
with two loops.
--
Ticket URL: <https://code.djangoproject.com/ticket/26565#comment:18>
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