Proper way to rename FK in django using south (postgress DB backend)

There is a problem in renaming FK keys using south in django when you are using postgres.

I tried this method:

db.rename_column('app_label', 'old_field_name_id', 'temp_old_field_name_id')

old_field_name_id pointed to custom user model.

The problem raised when I tried to create new field named 'old_field_name'  (pointing to model 'auth.User') and it said that field already exists. The problem raised because foreign-key constrants remained for 'old_field_name' and they should be recreated.

Proper way:

class Migration(SchemaMigration):

    def forwards(self, orm):
        from django.conf import settings

        table_name = 'users_address'
        old_field_name = 'user_id'
        new_field_name = 'old_user_id'

        if settings.DATABASES['default']['ENGINE'].endswith('psycopg2') or settings.DATABASES['default']['ENGINE'].endswith('postgis'):
            db.drop_foreign_key(table_name, old_field_name)
            db.delete_index(table_name, [old_field_name])
        db.rename_column(table_name, old_field_name, new_field_name)
        if settings.DATABASES['default']['ENGINE'].endswith('psycopg2') or settings.DATABASES['default']['ENGINE'].endswith('postgis'):
            db.alter_column(table_name, new_field_name, models.ForeignKey(null=True, to=orm['users.User']))
            db.create_index(table_name, [new_field_name])

    # you can easily find out how to write backward mibration yourself            
    

Notes: ForeignKey should point to model that original 'old_field_name' pointed to. 'null=True'