#28856: GenericForeignKey attributes create new instances on every access
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Reporter: Morgan Wahl | Owner: nobody
Type: Bug | Status: new
Component: | Version: 1.10
contrib.contenttypes |
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):
I'm pretty sure this is the expected behavior from `refresh_from_db()`,
refreshing any relationship should create a new instance as
`ref.refresh_from_db()` should roughly translate to `ref =
Ref.objects.get(pk=ref.pk)` while preserving `ref` identity.
e.g. foreign key relationships have always worked this way
{{{#!python
>> obj_type = ref.obj_type
>> ref.refresh_from_db()
>> ref.obj_type is obj_type
False
}}}
b9f8635f58ad743995cad2081b3dc395e55761e5 just made this consistent for
generic foreign key which wouldn't be refreshed before it landed. This was
a problem because if either `ref.obj_type` or `ref.obj_id` had changed
when `refresh_from_db()` was called then `ref.obj` would point to a
different object that the one referenced by `ref.obj_type` and
`ref.obj_id`.
Django's ORM doesn't maintain an identity mapping of object, as opposed to
SQL Alchemy for example, so you shouldn't expect refreshed instances to
share their identity.
--
Ticket URL: <https://code.djangoproject.com/ticket/28856#comment:3>
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