Django: Cannot resolve keyword '' into field. Choices are:

Question

I am having this weird problem accessing ManyToManyField.

I have following models.

class Link(models.Model):
    title = models.CharField(max_length = 200)
    url = models.URLField(unique = True)
    tags = models.ManyToManyField(Tag)
    creation_date = models.DateTimeField(auto_now_add = True)
    user = models.ForeignKey(User)
    likes = models.ManyToManyField(User, related_name = "%(app_label)s_%(class)s_user_likes")
    dis_likes = models.ManyToManyField(User, related_name = "%(app_label)s_%(class)s_user_dis_likes")

    class Meta:
        abstract = True

class URL(Link):
    preview_image = models.URLField()
    preview_heading = models.CharField(max_length = 100)
    preview_content = models.CharField(max_length = 100)

When I try to access URL.objects.get(pk=1).likes.all(), I get Cannot resolve keyword '' into field. Choices are:... error.

URL.objects.get(pk=1).tags.all(), URL.objects.get(pk=1).user and URL.objects.filter(likes=auser, pk=1) work fine.

Updates:

1. The fields likes and dis_likes were added using south through schemamigration
2. Previously I was using Django 1.6.1, updated to Django 1.6.2, the problem still persists
3. Truncated the database, synced it to have fresh tables, the problem still persists

4. Partial traceback:

   File "F:\system\env\lib\site-packages\django\db\models\manager.py" in all
     133.         return self.get_queryset()
   File "F:\system\env\lib\site-packages\django\db\models\fields\related.py" in get_queryset
     549.                 return super(ManyRelatedManager, self).get_queryset().using(db)._next_is_sticky().filter(**self.core_filters)
   File "F:\system\env\lib\site-packages\django\db\models\query.py" in filter
     590.         return self._filter_or_exclude(False, *args, **kwargs)
   File "F:\system\env\lib\site-packages\django\db\models\query.py" in _filter_or_exclude
     608.             clone.query.add_q(Q(*args, **kwargs))
   File "F:\system\env\lib\site-packages\django\db\models\sql\query.py" in add_q
     1198.         clause = self._add_q(where_part, used_aliases)
   File "F:\system\env\lib\site-packages\django\db\models\sql\query.py" in _add_q
     1234.                     current_negated=current_negated)
   File "F:\system\env\lib\site-packages\django\db\models\sql\query.py" in build_filter
     1100.                     allow_explicit_fk=True)
   File "F:\system\env\lib\site-packages\django\db\models\sql\query.py" in setup_joins
     1357.             names, opts, allow_many, allow_explicit_fk)
   File "F:\system\env\lib\site-packages\django\db\models\sql\query.py" in names_to_path
     1277.                                      "Choices are: %s" % (name, ", ".join(available)))
   
   Exception Type: FieldError at /url/3
   Exception Value: Cannot resolve keyword '' into field. Choices are: __app___article_user_dis_likes, __app___article_user_likes, __app___imageurl_user_dis_likes, __app___imageurl_user_likes, __app___review_user_dis_likes, __app___review_user_likes, __app___url_user_dis_likes, __app___url_user_likes, __app___videourl_user_dis_likes, __app___videourl_user_likes, article, date_joined, email, first_name, groups, id, imageurl, is_active, is_staff, is_superuser, last_login, last_name, logentry, password, review, url, user_permissions, username, userobjectpermission, videourl
   

Answer 1

I think I have found the problem. I suppose the problem is with the name of my app which is __app__. Django field look up assumes everything before __(double underscore) is a field which in my case resolves to ``(empty string).

Always had hard time naming the default app and the project it lives in. Thought __app__ was more pythonic and clever solution. I guess I should rename my app to just app. Hope this works.

Answer 2

This can happen if you attempt to use __unicode__ or __str__ in places where Django expects a field name. In my case I was trying to use __unicode__, because I give my models meaningful implementations and wanted to reuse it in the first column of tables.

To get around this I added

class AdminBase(admin.ModelAdmin):

    def natural_title(self, obj):
        return unicode(obj)

    natural_title.short_description = 'Title'

where AdminBase is a custom base class for my admin classes. I can now use 'natural_title' as a field name and get the results I was seeking.