#17003: prefetch_related should support foreign keys/one-to-one
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Reporter: lukeplant | Owner: nobody
Type: New feature | Status: new
Component: Database layer | Version: 1.3
(models, ORM) | Resolution:
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 0
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by mkai):
Perfect. Thanks! I've tested the patch with some actions from django-
activity-stream (see the Action model class: https://github.com/justquick
/django-activity-stream/blob/master/actstream/models.py). The Action model
defines three `GenericForeignKeys` and allows two of them to be NULL. So
do some of the instances currently in my database and so I managed to run
into the glorious "This should never happen" case ;)
The problem is in line 92 of django.contrib.contenttypes.generic, where
`getattr(obj, ct_attname)` returns `Null`. I haven't made a patch because
I wasn't sure whether it's better to check for a valid ContentType ID in
generic.py or in django.db.models.query, where the callable is evaluated.
For quick debugging, I gave `get_content_type` an id of 1, which already
reduced the number of queries from 76 to 53. So, aside from the Null
check, the patch seems to work fine for `GenericForeignKeys`.
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Ticket URL: <https://code.djangoproject.com/ticket/17003#comment:4>
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