How can I use South's DataMigration to change the storage backend of Django model ImageField instance?

I'm trying to migrate some models ImageFields to using the S3BotoStorage storage backend from django-storages. As part of this process I've changed my Model's ImageField declaration to include the storage=instance_of_s3botostorage argument, and new instances of my Model that save an image to the ImageField attribute now get stored in S3 - as intended.

I tried to move existing model instances over to开发者_Go百科 storing their data in S3, too, so wrote a South DataMigration like this:

def forwards(self, orm):
    "upload ImageField file to S3 if it's not already in there"
    for mymodel in orm.MyModel.objects.all():
        if mymodel.logo_image and not isinstance(mymodel.logo_image.storage, S3BotoStorage):
            print "uploading %s to S3" % mymodel.logo_image
            file_contents = ContentFile(mymodel.logo_image.read())
            mymodel.logo_image.save(mymodel.logo_image.name, file_contents)
            mymodel.save()

but this clearly doesn't have the intended effect because the image file is simply saved using the old storage backend - which makes sense considering save() is actually a method of the FieldFile belonging to the FileField

So, how to move/change file storage on an instance of a model?

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So, turns out the particular storage used for files is not stored in the database. 'migration' is simply a matter of changing the Model definition then, outside of using the storage subsystem API, simply upload files into the new storage locations.

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I would look at a system more like this for your problem. http://github.com/seanbrant/django-queued-storage