Using South HOWTO create an instance of a model from a different app during DataMigration

[Chintan Tank]

(sorry for duplicate I have already posted on stackoverflow.com >
http://goo.gl/I7Jj6 )

I need to perform a datamigration of a model Answer in app Question.
In that script there is a dependency such that I need to create an
instance of a model Chapter which is in the app Journal. So, I coded
it as follows:

def forwards(self, orm):
    for answer_object in orm.Answer.objects.all():

        #This Works.
        blog, is_created =
orm['blog.Post'].objects.get_or_create(title=answer_object.answer[:
100])
        blog.save()

        #This DOES NOT work
        chapter, is_created =
orm['journal.Chapter'].objects.get_or_create(content_object=blog)
        chapter.save()
        #cleanup task, not relevant to this question below
        answer_object.chapter_ptr = chapter
        answer_object.save()



But as expected this throws an error on "
orm['journal.Chapter'].objects.get_or_create(content_object=blog)"
saying that > django.core.exceptions.FieldError: Cannot resolve
keyword 'content_object' into field.

This is presumably due to content_object being a GenericForeignKey so
some operations are not allowed. But I also tried other alternatives
for creating the "chapter" object like,

chapter = orm['journal.Chapter'](content_object=blog)
ERROR > TypeError: 'content_object' is an invalid keyword argument for
this function

and

chapter = orm.journal.Chapter(content_object=blog)
ERROR > AttributeError: The model 'journal' from the app 'questions'
is not available in this migration. (Did you use orm.ModelName, not
orm['app.ModelName']?)

So since my earlier approach was failing I tried a new tact. The model
whose instantiation was failing in my code above i.e. Chapter in the
Journal app, I decided to create a datamigration for that instead. I
also made sure to --freeze the models I am referring to in the
forwards definition. Now this should have been straight forward, I
would think. I have my forward code as follows -

def forwards(self, orm):

    for answer_object in orm['questions.Answer'].objects.all():

        #Works, AGAIN!
        blog, is_created =
orm['blog.Post'].objects.get_or_create(title=answer_object.answer[:
100])
        blog.save()

        # DOES NOT WORK, AGAIN!
        chapter = orm.Chapter(rank=1, content_object=blog)
        chapter.save()


I would have thought that now since I am creating instance of a model
(Chapter) which exists in the subject app (Journal) everything should
have worked out. But i am getting the same error > TypeError:
'content_object' is an invalid keyword argument for this function.

It fails at the same point, namely, "content_object". I will post
below the model definition if that might help.

class Chapter(models.Model):

    rank = models.IntegerField()

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey()

Also all the models being touched in these forwards methods, namely -
blog, chapter, questions; are fully defined in the 00n_*.py files
created by South's schemamigration.





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