Django migrations with foreign key

Question

I' trying to migrate this model:

class Questionpart_image(models.Model):
    questionpart = models.ForeignKey(Questionpart, null=True, blank=True)
    image = models.ImageField()

to this:

class Questionpart_image(Questionpart): # notice this base class
    image = models.ImageField()

to make advantage of inheritance. Django produces the following migration:

class Migration(migrations.Migration):

dependencies = [
    ('ochsite', '0016_auto_20150809_1903'),
]

operations = [
    migrations.RemoveField(
        model_name='questionpart_image',
        name='id',
    ),
    migrations.RemoveField(
        model_name='questionpart_image',
        name='questionpart',
    ),
    migrations.AddField(
        model_name='questionpart_image',
        name='questionpart_ptr',
        field=models.OneToOneField(default='', primary_key=True, to='ochsite.Questionpart', serialize=False, parent_link=True, auto_created=True),
        preserve_default=False,
    ),
]

but this does not set the right foreign key to questionpart_ptr from questionpart field. How can I achieve that?
I've been searching for a long time, but nothing...thanks

Answer 1

Simply don't rely on automatic migrations, make your own or modify that one.

Simplest solution will be by moving AddField in migration to the top of the list and inject between it and RemoveField s RunPython block that will rewrite id's from old field to new (and in other direction in reverse, if needed).