id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
8569	"Admin fieldsets can cause ""'str' object has no attribute '_default_manager'' under mod_wsgi"	Karen Tracey	Malcolm Tredinnick	"As reported here: http://groups.google.com/group/django-users/browse_thread/thread/da39ac4b1e5c1751# (and earlier but never recreated/isolated), under some circumstances a fieldsets definition in a !ModelAdmin definition can cause the exception: 

'str' object has no attribute '_default_manager'

Today's poster isolated the problem to mod_wsgi, and I was able to recreate with an example project he sent to me.  There are two apps: catalogue and simplepromo (listed in that order in INSTALLED_APPS, reversing them didn't change anything).  catalogue has a single model in models.py:

{{{
class Maker(models.Model):
    dummy = models.CharField(blank=True, max_length=80)

    def __unicode__(self):
        return self.dummy
}}}

simplepromo (a simplified version of what Maciek sent me), also has a single model in models.py:

{{{
class SimplePromo(models.Model):
    
    name = models.CharField(blank=False, max_length=250, help_text=""Displayed in overlay tooltip"")
    slug = models.SlugField()
    promo_maker = models.ForeignKey(""catalogue.Maker"", null=True, blank=False)
    def __unicode__(self):
        return self.name
}}}

and an admin.py file:

{{{
from django.contrib import admin
from simplepromo.models import *
class SimplePromoAdmin(admin.ModelAdmin):
    prepopulated_fields = {'slug': ('name',)}
    
    fieldsets = (
        (""Base"", {
            ""fields"": [""name"",""slug"",""promo_maker"",],
        }),
    )
    
admin.site.register(SimplePromo, SimplePromoAdmin)
}}}

The call to admin.autodiscover() in urls.py is what generates the exception.  If I remove the catch/transform to !ImproperlyConfigured done by urlresolvers.py (ref #7524) I can get the actual traceback:

{{{
Environment:

Request Method: GET
Request URL: http://localhost/admin/
Django Version: 1.0-beta_1-SVN-8582
Python Version: 2.5.2
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.humanize',
 'django.contrib.markup',
 'django.contrib.sessions',
 'django.contrib.sites',
 'catalogue',
 'simplepromo']
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.middleware.doc.XViewMiddleware')


Traceback:
File ""c:\u\kmt\django\trunk\django\core\handlers\base.py"" in get_response
  77.                     request.path_info)
File ""c:/u/kmt/django/trunk\django\core\urlresolvers.py"" in resolve
  238.             for pattern in self.urlconf_module.urlpatterns:
File ""c:/u/kmt/django/trunk\django\core\urlresolvers.py"" in _get_urlconf_module
  257.              self._urlconf_module = __import__(self.urlconf_name, {}, {}, [''])
File ""c:/u/kmt/software/web/ppi-test\urls.py"" in <module>
  9. admin.autodiscover()
File ""c:\u\kmt\django\trunk\django\contrib\admin\__init__.py"" in autodiscover
  19.         __import__(""%s.admin"" % app)
File ""c:/u/kmt/software/web/ppi-test\simplepromo\admin.py"" in <module>
  12. admin.site.register(SimplePromo, SimplePromoAdmin)
File ""c:\u\kmt\django\trunk\django\contrib\admin\sites.py"" in register
  91.             validate(admin_class, model)
File ""c:\u\kmt\django\trunk\django\contrib\admin\validation.py"" in validate
  19.     _validate_base(cls, model)
File ""c:\u\kmt\django\trunk\django\contrib\admin\validation.py"" in _validate_base
  201.             _check_form_field_existsw(""fieldsets[%d][1]['fields']"" % idx, field)
File ""c:\u\kmt\django\trunk\django\contrib\admin\validation.py"" in _check_form_field_existsw
  162.         return _check_form_field_exists(cls, model, opts, label, field)
File ""c:\u\kmt\django\trunk\django\contrib\admin\validation.py"" in _check_form_field_exists
  282.         fields = fields_for_model(model)
File ""c:\u\kmt\django\trunk\django\forms\models.py"" in fields_for_model
  145.         formfield = formfield_callback(f)
File ""c:\u\kmt\django\trunk\django\forms\models.py"" in <lambda>
  124. def fields_for_model(model, fields=None, exclude=None, formfield_callback=lambda f: f.formfield()):
File ""c:\u\kmt\django\trunk\django\db\models\fields\related.py"" in formfield
  726.         defaults = {'form_class': forms.ModelChoiceField, 'queryset': self.rel.to._default_manager.complex_filter(self.rel.limit_choices_to)}

Exception Type: AttributeError at /admin/
Exception Value: 'str' object has no attribute '_default_manager'
}}}

I added a couple of local variables so I could see what's what and the local vars in that last routine are:

{{{
kwargs  {}
self  <django.db.models.fields.related.ForeignKey object at 0x01EC8390>
self_rel <django.db.models.fields.related.ManyToOneRel object at 0x01EC83B0>
self_rel_to 'catalogue.Maker'
}}}

Running the exact same app code under the development server plus putting a stop exception where the exception is generated under wsgi, I can see the local vars are different when running under the dev server:

{{{
kwargs  {}
self  <django.db.models.fields.related.ForeignKey object at 0x01067BB0>
self_rel  <django.db.models.fields.related.ManyToOneRel object at 0x01067BD0>
self_rel_to  <class 'catalogue.models.Maker'>
}}}

So somehow when running under the dev server (and anything other than wsgi, according to Maciek) self.rel.to has been transformed from a string to an actual class reference before this code is called.  I haven't a clue how this happens or why it isn't happening when running under mod_wsgi, so that's about as far as I can go with this one.  Hopefully someone else can shed some light?"		closed	Uncategorized	dev		fixed			Unreviewed	0	0	0	0	0	0