#25374: Admin system check prevents dynamic ModelAdmin attributes
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Reporter: mbox | Owner: nobody
Type: Bug | Status: new
Component: contrib.admin | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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With a ModelAdmin that defines some dynamic attributes via __getattr__,
and uses these in fields or readonly_fields (or list_display etc), the
system check admin.E035 error is raised.
Simple example below - note that in the full use case, the __getattr__ is
part of a baseclass/mixin so it can be reused across multiple ModelAdmins
:
{{{
class ExampleAdmin(models.ModelAdmin):
fields = ['image_thumbnail', 'image', 'another_image',
'another_image_thumbnail']
readonly_fields = ['image_thumbnail', 'another_image_thumbnail']
list_display = ['image_thumbnail']
def __getattr__(self, name):
if name.endswith('_thumbnail'):
def thumbnail_function(obj):
# ... generate appropriate thumbnail method
return thumbnail_function
else:
raise AttributeError
}}}
This code worked fine in 1.6, and it works fine in 1.8/1.9 if the system
check is silenced.
The root cause is that the system check uses the class to verify that
fields exist rather than an instance:
https://github.com/django/django/blob/dae81c6ec62a76c1f28745ae3642c2d4a37ce259/django/contrib/admin/sites.py#L106-L110
Which means that anything that's defined on an instance of the ModelAdmin
but not on the class itself will fail the check, whereas the code will
work.
According to the documentation, for readonly_fields, the values are
"similar to list_display", and list_display is documented to allow "A
string representing an attribute on the ModelAdmin". However this fails
system check admin.E108
There's two issues raised by this:
* Is it reasonable for system checks to fail when the actual code will
work - or is this *always* a bug in the system check?
* In this specific case, should the admin system check inspect ModelAdmin
instances rather than classes so that the check is closer to the
implementation.
--
Ticket URL: <https://code.djangoproject.com/ticket/25374>
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