django-mptt and change model instance parent

[Дмитрий Чернышов]

I have a little problem with django-mptt 0.6.0. I have model MyModel with standard parent field and register as mptt-model through mptt.register(MyModel). I create MyModel instance obj_1 with None parent as 0 level object. After this i create MyModel instance obj_2 with None parent also as 0 level object. I try to change obj_2 parent value from None to obj_1. When I call save method of obj_2, mptt raise

AttributeError: 'NoneType' object has no attribute 'tree_id'.

Problem at mptt/models.py:782 line, where we try do this:

getattr(self, opts.tree_id_attr) != getattr(parent, opts.tree_id_attr)

This error raised, because before this we have 2 step:

1. opts.set_raw_field_value(self, opts.parent_attr, old_parent_id) - where old_parent_id is None
2. parent = getattr(self, opts.parent_attr) - where parent, of course, also is None

Is that bug?

[Craig de Stigter]

I see this was a week ago, did you get any further with it?

It works for me with this code:

In [16]: o1 = Category()
In [17]: o2 = Category()
In [18]: o1.save()
In [19]: o2.parent = o1
In [20]: o2.save()

If you didn't get it working could you paste your code and your model? And probably a full traceback too.

Thanks, sorry it took me a week to get this far.

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[Arthur Mullakhmetov]

It seems that setting parent_id does not reset parent in any way, resp. parent isn't dynamically loaded from the database just because the underlying id field has some value.

https://github.com/django-mptt/django-mptt/issues/428