#15804: Query lookup types should be scoped to the last joined field's model
-------------------------------------+-------------------------------------
Reporter: adrian | Owner: nobody
Type: Bug | Status: new
Milestone: | Component: Database layer
Version: 1.3 | (models, ORM)
Resolution: | Severity: Normal
Triage Stage: Design | Keywords:
decision needed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 |
-------------------------------------+-------------------------------------
Description changed by adrian:
Old description:
> This is kind of obscure and best described by example. I have two models:
>
> {{{
> from django.db import models
> from django.contrib.gis.db import models as geo_models
>
> # Note this is a geo-aware model.
> class Place(geo_models.Model):
> geom = geo_models.GeometryField()
>
> # Note this is NOT a geo-aware model.
> class Person(models.Model):
> name = models.CharField(max_length=50)
> hometown = models.ForeignKey(Place)
> }}}
>
> I'd like to be able to do this:
>
> {{{
> Person.objects.filter(hometown__geom__intersects=some_geometry)
> }}}
>
> ...but that doesn't work. It gives me this error:
>
> {{{
> django.core.exceptions.FieldError: Join on field 'geom' not permitted.
> Did you misspell 'intersects' for the lookup type?
> }}}
>
> This happens because {{{Person}}} isn't a geo-aware model, so it doesn't
> know that {{{__intersects}}} is a valid lookup type. I can fix it by
> changing {{{Person}}} to extend {{{django.contrib.gis.db.models}}}, but
> that feels hacky because the {{{Person}}} model itself doesn't have any
> geo fields.
>
> The solution could be to change Django's join code so that it looks at
> the model of the last field in the chain when determining whether a
> lookup is valid. I haven't looked into how difficult this would be,
> though. I think it's just enough of an edge case that it wouldn't be
> worth fixing if it required a ton of refactoring and hoop-jumping. But if
> it's easy, let's do it.
New description:
This is kind of obscure and best described by example. I have two models:
{{{
from django.db import models
from django.contrib.gis.db import models as geo_models
# Note this is a geo-aware model.
class Place(geo_models.Model):
geom = geo_models.GeometryField()
# Note this is NOT a geo-aware model.
class Person(models.Model):
name = models.CharField(max_length=50)
hometown = models.ForeignKey(Place)
}}}
I'd like to be able to do this:
{{{
Person.objects.filter(hometown__geom__intersects=some_geometry)
}}}
...but that doesn't work. It gives me this error:
{{{
django.core.exceptions.FieldError: Join on field 'geom' not permitted. Did
you misspell 'intersects' for the lookup type?
}}}
This happens because {{{Person}}} isn't a geo-aware model, so it doesn't
know that {{{__intersects}}} is a valid lookup type. I can fix it by
changing {{{Person}}} to extend {{{django.contrib.gis.db.models}}} and
adding the {{{GeoManager}}}, but that feels hacky because the {{{Person}}}
model itself doesn't have any geo fields.
The solution could be to change Django's join code so that it looks at the
model of the last field in the chain when determining whether a lookup is
valid. I haven't looked into how difficult this would be, though. I think
it's just enough of an edge case that it wouldn't be worth fixing if it
required a ton of refactoring and hoop-jumping. But if it's easy, let's do
it.
--
--
Ticket URL: <http://code.djangoproject.com/ticket/15804#comment:1>
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