Filtering query using django geographical span relationship is not accepted

Question

I'm trying to filter some item using a geographical span relationship with geodjango, but I don't get why it doesn't work. Consider this example:

class Location(models.Model):
    name = models.CharField(max_length=32,)
    marker = models.PointField(srid=4326) # the marker
    objects = models.GeoManager()

class Item(models.Model):
    name =  models.CharField(max_length=200)
    location = models.ForeignKey(Location)


poly = Polygon(
[(0.02780914306640625, 52.158980248467095),
 (0.22350311279296875, 52.158980248467095),
 (0.22350311279296875, 52.253657959623055),
 (0.02780914306640625, 52.253657959623055),
 (0.02780914306640625, 52.158980248467095)]
)

If I query for ("A location" is an existing location in the db)

Item.objects.filter(location__name__exact="A location")

it works.

If instead I query for

Item.objects.filter(location__marker__within=poly)

I get this error

---------------------------------------------------------------------------
FieldError                                Traceback (most recent call last)
/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/core/management/commands/shell.pyc in <module>()
----> 1 Item.objects.filter(location__marker__within=poly)

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/manager.pyc in filter(self, *args, **kwargs)
    141 
    142     def filter(self, *args, **kwargs):
--> 143         return self.get_query_set().filter(*args, **kwargs)
    144 
    145     def aggregate(self, *args, **kwargs):

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/query.pyc in filter(self, *args, **kwargs)
    619         set.
    620         """
--> 621         return self._filter_or_exclude(False, *args, **kwargs)
    622 
    623     def exclude(self, *args, **kwargs):

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/query.pyc in _filter_or_exclude(self, negate, *args, **kwargs)
    637             clone.query.add_q(~Q(*args, **kwargs))
    638         else:
--> 639             clone.query.add_q(Q(*args, **kwargs))
    640         return clone
    641 

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in add_q(self, q_object, used_aliases, force_having)
   1248                 else:
   1249                     self.add_filter(child, connector, q_object.negated,
-> 1250                             can_reuse=used_aliases, force_having=force_having)
   1251                 if force_having:
   1252                     self.having.end_subtree()

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in add_filter(self, filter_expr, connector, negate, trim, can_reuse, process_extras, force_having)
   1120                     parts, opts, alias, True, allow_many, allow_explicit_fk=True,
   1121                     can_reuse=can_reuse, negate=negate,
-> 1122                     process_extras=process_extras)
   1123         except MultiJoin, e:
   1124             self.split_exclude(filter_expr, LOOKUP_SEP.join(parts[:e.level]),

/home/mattions/.virtualenvs/ssouk_env/local/lib/python2.7/site-packages/django/db/models/sql/query.pyc in setup_joins(self, names, opts, alias, dupe_multis, allow_many, allow_explicit_fk, can_reuse, negate, process_extras)
   1473         if pos != len(names) - 1:
   1474             if pos == len(names) - 2:
-> 1475                 raise FieldError("Join on field %r not permitted. Did you misspell %r for the lookup type?" % (name, names[pos + 1]))
   1476             else:
   1477                 raise FieldError("Join on field %r not permitted." % name)

FieldError: Join on field 'marker' not permitted. Did you misspell 'within' for the lookup type?

Note that

Location.objects.filter(marker__within=poly)

works as expected

Is there any way to do this across a relationship?

Answer 1

It turns out that the answer was given on the geodjango mailinglist ( https://groups.google.com/forum/?fromgroups=#!topic/geodjango/wvEJaYX_Cuc ), so I'll write here as well if somebody stumbles on it

If you need to use a geoQueryset on a span relationship, you need to use the GeoManager also on the model that does not have spatial feature, but ForeignKey to a models with an attribute as class.

Therefore the correct way is from django.contrib.gis.db import models

class Location(models.Model):
    name = models.CharField(max_length=32,)
    marker = models.PointField(srid=4326) # the marker
    objects = models.GeoManager()

class Item(models.Model):
    name =  models.CharField(max_length=200)
    location = models.ForeignKey(Location)
    objects = models.GeoManager()

and then the Item.objects.filter(location__marker__within=poly)works as expected.