#32511: Deferred fields incorrect when following prefetches back to the "parent"
object
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Reporter: Jamie Matthews | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.1
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| 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 Simon Charette):
When using `prefetch_related` the retrieved objects are assigned their
origin's foreign object so in this case the inner prefetch is performed
but entirely discarded because it's the outer's query `user` (the ones
with ''only'' `email`) that are assigned to the prefetched profiles.
I guess we should either change the current behaviour to default to using
the origin's object but allow overrides with nested prefetches as it might
be useful when dealing with graphs of objects or raise an exception in
this case to denote this isn't supported.
I think you'll want to look at this branch of `prefetch_one_level` to
special case already cached instances
https://github.com/django/django/blob/b19041927883123e0147d80b820ddabee9a716f6/django/db/models/query.py#L1905-L1913
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Ticket URL: <https://code.djangoproject.com/ticket/32511#comment:1>
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