#28490: Descriptors on Models are reported as nonexistent by System Check
Framework
for ModelAdmin.list_display if they return None
-------------------------------------+-------------------------------------
Reporter: Hunter Richards | Owner: nobody
Type: Bug | Status: closed
Component: contrib.admin | Version: master
Severity: Normal | Resolution: fixed
Keywords: admin, descriptor, | Triage Stage: Accepted
system, checks, framework, |
validation |
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by ajcsimons):
Unfortuantely this fix causes other bugs:
1. if hasattr(obj.model, item) returns false then we go straight to the
else clause which returns the error,
2. whereas before the else clause did another check for
model._meta.get_field(item) and would only return the error if that raised
a FieldDoesNotExist exception
3. So how is it that hasattr(model, item) can return false, but
model._meta.get_field(item) will return something meaning the check should
not return an error?
4. Answer: the field is a special one which is only valid to access on
instances of the model (whose ModelAdmin we are verifying) and not the
model class itself. An example of this is the PositionField from the
django-positions library (which inherits from djangos
models.IntegerField):
{{{
def __get__(self, instance, owner):
if instance is None:
raise AttributeError("%s must be accessed via instance." %
self.name)
current, updated = getattr(instance, self.get_cache_name())
return current if updated is None else updated
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/28490#comment:6>
Django <https://code.djangoproject.com/>
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