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
12237	Attempting to use a ManyToManyField with 'through' in ModelAdmin gives uninformative help message if using `fieldsets`	Pyth	Ramiro Morales	"Attempting to use a `ManyToManyField` with 'through' in `ModelAdmin` gives an uninformative help message if `fieldsets` are used to select the fields to use in the form instead of `fields`.  I've confirmed this problem in the latest SVN revision, r11743.

== Sample models ==

Here are three models with a `ManyToManyField` relationship declared via `through`.

{{{
#!python
class Person(models.Model):
    name = models.CharField(max_length=128)

    def __unicode__(self):
        return self.name

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(Person, through='Membership')

    def __unicode__(self):
        return self.name

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=64)
}}}

== Helpful error when using `fields` ==

Creating an admin model using `fields` to construct it gives an extremely helpful error message when attempting to use the `members` field in the form.

{{{
#!python
class GroupAdmin(admin.ModelAdmin):
    fields = ('name', 'members')
}}}

'''Error:''' `ImproperlyConfigured: 'GroupAdmin.fields' can't include the ManyToManyField field 'members' because 'members' manually specifies a 'through' model.`

== Less helpful error when using `fieldsets` ==

However, doing the same thing with a `fieldsets` approach will give the user a much more confusing error.

{{{
#!python
class GroupAdmin(admin.ModelAdmin):
    fieldsets = (
        (None, {'fields': ('name', 'members')}),
    )
}}}

'''Error:''' `Caught an exception while rendering: 'NoneType' object has no attribute 'label'`

The traceback isn't excessivley informative either:

{{{
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/core/handlers/base.py"" in get_response
  99.                     response = callback(request, *callback_args, **callback_kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/contrib/admin/options.py"" in wrapper
  228.                 return self.admin_site.admin_view(view)(*args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/utils/decorators.py"" in __call__
  36.         return self.decorator(self.func)(*args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/utils/decorators.py"" in _wrapped_view
  86.                     response = view_func(request, *args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/utils/decorators.py"" in __call__
  36.         return self.decorator(self.func)(*args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/views/decorators/cache.py"" in _wrapped_view_func
  70.         response = view_func(request, *args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/contrib/admin/sites.py"" in inner
  187.             return view(request, *args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/utils/decorators.py"" in _wrapped_view
  86.                     response = view_func(request, *args, **kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/db/transaction.py"" in _commit_on_success
  240.                 res = func(*args, **kw)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/contrib/admin/options.py"" in add_view
  788.         return self.render_change_form(request, context, form_url=form_url, add=True)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/contrib/admin/options.py"" in render_change_form
  592.         ], context, context_instance=context_instance)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/shortcuts/__init__.py"" in render_to_response
  20.     return HttpResponse(loader.render_to_string(*args, **kwargs), **httpresponse_kwargs)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/loader.py"" in render_to_string
  108.     return t.render(context_instance)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  178.         return self.nodelist.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  779.                 bits.append(self.render_node(node, context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/debug.py"" in render_node
  71.             result = node.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/loader_tags.py"" in render
  97.         return compiled_parent.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  178.         return self.nodelist.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  779.                 bits.append(self.render_node(node, context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/debug.py"" in render_node
  71.             result = node.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/loader_tags.py"" in render
  97.         return compiled_parent.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  178.         return self.nodelist.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  779.                 bits.append(self.render_node(node, context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/debug.py"" in render_node
  71.             result = node.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/loader_tags.py"" in render
  24.         result = self.nodelist.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  779.                 bits.append(self.render_node(node, context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/debug.py"" in render_node
  71.             result = node.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/defaulttags.py"" in render
  172.                 nodelist.append(node.render(context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/loader_tags.py"" in render
  111.             return self.template.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  178.         return self.nodelist.render(context)
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/__init__.py"" in render
  779.                 bits.append(self.render_node(node, context))
File ""/Users/corona/.virtualenvs/grapewire/src/django-trunk/django/template/debug.py"" in render_node
  81.             raise wrapped
}}}"		closed	contrib.admin	dev		fixed			Accepted	1	0	0	0	0	0