`ForeignKeyField` nonsupport 'self'

[daixijun]

models.py

class Group(BaseModel):
    name = pw.CharField(max_length=255, null=False, unique=True)
    parent = pw.ForeignKeyField('self', null=True, related_name='children')
    description = pw.CharField(max_length=255, null=True)

    def __str__(self):
        return self.name

migrations/001_auth.py

def migrate(migrator, database, fake=False, **kwargs):

    @migrator.create_model
    class Group(pw.Model):
        name = pw.CharField(max_length=255, unique=True)
        parent = pw.ForeignKeyField(db_column='parent_id', rel_model=migrator.orm['group'], related_name='children', to_field='id')
        description = pw.CharField(max_length=255, null=True)

        class Meta:
            db_table = "group"

errors

➜  ams-api git:(master) ✗ python manage.py migrate
Traceback (most recent call last):
  File "manage.py", line 71, in <module>
    cli()
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "manage.py", line 32, in migrate
    migrations = router.run(name, fake=False)
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/peewee_migrate/router.py", line 170, in run
    self.run_one(mname, migrator, fake=fake, force=fake)
  File "/Users/tux/.pyenv/versions/3.6.1/envs/sanic-ams-api/lib/python3.6/site-packages/peewee_migrate/router.py", line 140, in run_one
    migrate(migrator, self.database, fake=fake)
  File "<string>", line 94, in migrate
  File "<string>", line 96, in Group
KeyError: 'group'