Migrating existing model data to MPTTModel?

Question

Django

There is a data model. Installed django-mptt, but how do I now migrate data from the old model to the new MPTTModel?

Tag(models.Model):
    name = models.CharField(u'Название', max_length=255, unique=True)
    parent = models.ForeignKey('self', verbose_name='Родительский тег', null=True, blank=True, related_name='children')

do:

Tag(MPTTModel):
    name = models.CharField(u'Название', max_length=255, unique=True)
    parent = TreeForeignKey('self', on_delete=models.CASCADE, verbose_name='Родительский тег', null=True, blank=True, related_name='children')

When I do makemigrations, I am asked to put in default values, but after migrate all tags turn into single-level tags, without nested tags.

Answer 1

$ python manage.py shell

In [1]: from some_app.models import Tag
In [2]: Tag.objects.rebuild()