#25299: Backwards compatibility issue with list_display callable names
-------------------------------+----------------------------------------
Reporter: scoenye | Owner: nobody
Type: Bug | Status: new
Component: Uncategorized | Version: 1.8
Severity: Normal | Keywords: list_display callable name
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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In contrast to Django 1.7, Django 1.8 does not allow callables in
list_display to have the same name as a relation related_name on a model.
Starting with
{{{
class SupportItem(models.Model):
description = models.CharField(max_length=30)
class Hardware(SupportItem):
tag = models.IntegerField(unique=True)
}}}
and
{{{
class Placement(models.Model):
support_item = models.ForeignKey("SupportItem")
place_date = models.DateTimeField()
location = models.CharField(max_length=50, null=True, blank=True)
}}}
I have defined a view on the database exposed in Django as
{{{
class HardwareLastAssigned(models.Model):
hardware = models.OneToOneField(Hardware, primary_key=True,
db_column='support_item_id',
related_name='last_assigned')
location = models.CharField(max_length=50, blank=True)
}}}
which gives the last location a hardware item was deployed to.
Under Django 1.7, the following admin code produces a changelist showing
each piece of hardware and its current location:
{{{
class HardwareAdmin(NavigableModelAdmin):
list_display = ['tag', 'placement']
list_display_links = list_display
search_fields = ['tag', 'last_assigned__location']
form = HardwareForm
...
def placement(self, obj):
return obj.last_assigned.location
def get_queryset(self, request):
hardware = super(HardwareAdmin, self).get_queryset(request)
hardware = hardware.select_related("last_assigned")
return hardware
}}}
Following an upgrade to Django 1.8, the same code crashes with this
exception:
AttributeError: 'Hardware' object has no attribute 'placement'
in
File "/home/django/python2.7-django1.8/lib/python2.7/site-
packages/django/contrib/admin/utils.py", line 288, in lookup_field
value = getattr(obj, name)
The cause lies in Options.get_field() (django.db.models.options) which
under 1.7 only recognized true fields on the model at hand (Hardware),
whereas under 1.8, it also reports related models as fields on the model.
However, lookup_field can only handle true fields and triggers the
exception.
A workaround is to rename the callable so it does not match any related
names which may be associated with the model.
The change was made in commit fb48eb05816b1ac87d58696cdfe48be18c901f16 as
part of the formalizations of the _meta API.
If nothing else can be done, it may be worth a mention in the list_display
documentation as this restriction is not at all obvious (to me) based on
the current docs and the 1.8 release notes.
--
Ticket URL: <https://code.djangoproject.com/ticket/25299>
Django <https://code.djangoproject.com/>
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