Can't save model with ManyToMany Field

I’ve found a bug in save of m2m related objects. Steps to reproduce:

• Install wagtail CMS
• Create single Page model
• Create standard Django model
• Add ManyToManyField from your Page model to standard django model
• Try to create page instance

When you try to save it, you’ll receive following error:

Traceback:
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  114.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  22.                 return view_func(request, *args, **kwargs)
File "/home/artur/Projekty/demo/src/wagtail/wagtail/wagtailadmin/views/pages.py" in create
  172.             page = form.save(commit=False)  # don't save yet, as we need treebeard to assign tree params
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/modelcluster/forms.py" in save
  257.             self.save_m2m()
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/forms/models.py" in save_m2m
  96.                 f.save_form_data(instance, cleaned_data[f.name])
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in save_form_data
  1527.         setattr(instance, self.attname, data)
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __set__
  835.         manager = self.__get__(instance)
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __get__
  825.             through=self.field.rel.through,
File "/home/artur/Projekty/demo/local/lib/python2.7/site-packages/django/db/models/fields/related.py" in __init__
  522.                                  (instance, source_field_name))

It tries to execute save_m2m() before saving page instance. Is there workaround for this issue?

[gasman]

Finally completed in #62!

[alexgleason]

I wrote a quick guide and explanation on how to implement M2M’s using what’s currently available. https://gist.github.com/alexgleason/09b1802b004babd74e96