Update mptt.rst

[zhangguiyu]

minor edits to mptt example

[vdboor]

Hi! Thanks for updating the docs!
Do you know which version of mptt is affected by this? I didn't see this happening before.

[zhangguiyu]

Hi Vdboor,

I am using django-mptt==0.7.4 with django-parler==1.5

If I put MPTTModel in second position in my abstract model, i.e.,

class AbstractNode(AbstractModel, MPTTModel):

, I get errors like

Traceback (most recent call last):
  File "./manage.py", line 10, in 
    execute_from_command_line(sys.argv)
  File "/pythonenv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/pythonenv/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 312, in execute
    django.setup()
  File "/pythonenv/local/lib/python2.7/site-packages/django/__init__.py", line 18, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/pythonenv/local/lib/python2.7/site-packages/django/apps/registry.py", line 108, in populate
    app_config.import_models(all_models)
  File "/pythonenv/local/lib/python2.7/site-packages/django/apps/config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/data/gits/irc/src/irc/models.py", line 18, in 
    from irc.abstract import *
  File "/data/gits/irc/src/irc/abstract.py", line 158, in 
    class AbstractNode(AbstractModel, MPTTModel):
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/base.py", line 189, in __new__
    new_class.add_to_class(obj_name, obj)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/base.py", line 324, in add_to_class
    value.contribute_to_class(cls, name)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 1778, in contribute_to_class
    super(ForeignObject, self).contribute_to_class(cls, name, virtual_only=virtual_only)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 313, in contribute_to_class
    add_lazy_relation(cls, self, other, resolve_related_class)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 86, in add_lazy_relation
    operation(field, model, cls)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 312, in resolve_related_class
    field.do_related_class(model, cls)
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 355, in do_related_class
    self.set_attributes_from_rel()
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 345, in set_attributes_from_rel
    self.rel.set_field_name()
  File "/pythonenv/local/lib/python2.7/site-packages/django/db/models/fields/related.py", line 1432, in set_field_name
    self.field_name = self.field_name or self.to._meta.pk.name
AttributeError: 'NoneType' object has no attribute 'name'

However, if I put MPTTModel first, it works, i.e.,

class AbstractNode(MPTTModel, AbstractModel):

P.S. I am following the same approach as django-categories-i18n, which also listed MPTTModel first:

#categories_i18n/abstract.py
class AbstractCategory(MPTTModel, TranslatableModel):

[vdboor]

Good to know! If you can update the pull request, I'll merge it!

[zhangguiyu]

I have updated the pull request with a switch that checks for MPTT version. Should work now with Travis CI with various MPTT versions.

[vdboor]

I've merged your changes in cb12319!
The MPTTQuerySet code had to be removed, there is nu such class in the django-mptt git history.

Thanks for the work, and bringing the issues of the docs to our attention!

[zhangguiyu]

Thanks!