Django-mptt form "Attribute error"

Question

I created a class as described in the mptt docs

class Locations(MPTTModel):
    title = models.CharField(max_length=100)
    parent = TreeForeignKey('self', null=True, blank=True, related_name='children')

    def __unicode__(self):
        return self.title

I'm doing a form as written in the manual

class RealtyAdminModelForm(forms.ModelForm):
    location = TreeNodeChoiceField(queryset=Locations.tree.all(),
                                   level_indicator=u'+--')
class Meta:
    model = Realty

But django gives the following error: type object 'Locations' has no attribute 'tree'

Why is this so?

Answer 1

I don't understand why in docs (http://django-mptt.github.io/django-mptt/forms.html) "tree", but the right is "objects":

class RealtyAdminModelForm(forms.ModelForm):
    location = TreeNodeChoiceField(queryset=Locations.objects.all(),
                                   level_indicator=u'+--')
class Meta:
    model = Realty