Little change of admin filter URL throws AttributeError

[Vlada Macek]

A list_filter for FK creates a query string <field>__id__exact. Changing 'exact' to anything else appears to throw:

AttributeError: 'NoneType' object has no attribute 'to'

Tested on 1.5.4 and 1.4.x.

.../django/contrib/admin/options.py in lookup_allowed
                try:
                    field, _, _, _ = model._meta.get_field_by_name(part)
                except FieldDoesNotExist:
                    # Lookups on non-existent fields are ok, since they're ignored
                    # later.
                    return True
                if hasattr(field, 'rel'):
>>>                 model = field.rel.to
                    rel_name = field.rel.get_related_field().name
                elif isinstance(field, RelatedObject):
                    model = field.model
                    rel_name = model._meta.pk.name
                else:
                    rel_name = None

▼ Local vars
Variable 	Value
rel_name 	u'id'
self 	<project.apps.calendar.admin.BusyAdmin object at 0xb523768c>
parts 	[u'site', u'id', u'anything']
value 	u'5'
field 	<django.db.models.fields.AutoField: id>
part 	u'id'
lookup 	u'site__id__anything'
model 	<class 'django.contrib.sites.models.Site'>
_ 	False

[Tim Graham]

I guess the solution here would be to ignore the invalid parameter rather than throw a server error?

[Timothy Schilling]

Alright I think I have a decent solution. One thing I want to bring up is that when you attempt to use a URL that has a bad filter, it will redirect you to the same page but with the query string set to ?e=1. I looked this up and it looks like it means that an error occurred. Is this the correct response? I suppose it lets the user know that they requested a bad url, but it eliminates the query string they had previously.

I created a simple test to verify this new functionality in the method lookup_allowed

Commit: ​https://github.com/tim-schilling/django/commit/a143239afd9faaa3317e1447e761faa02a778056

[Tim Graham <timograham@…>]

In 5381317fe37d50384ef9a3bf3fb6b64ff4e9215c:

Fixed #21129 -- Prevented admin filter params modifications from throwing an exception.

Thanks Tuttle for the report.

[Tim Graham <timograham@…>]

In e5b0f5b95d49c33f5431cf4060705b5e59ec69d4:

[1.6.x] Fixed #21129 -- Prevented admin filter params modifications from throwing an exception.

Thanks Tuttle for the report.

Backport of 5381317fe3 from master