Quando eupython3 manage.py makemigrations, Recebo o seguinte erro:

...

  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/db/models/fields/related.py", line 348, in contribute_to_class
    lazy_related_operation(resolve_related_class, cls, self.remote_field.model, field=self)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/db/models/fields/related.py", line 85, in lazy_related_operation
    return apps.lazy_model_operation(partial(function, **kwargs), *model_keys)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/db/models/fields/related.py", line 83, in <genexpr>
    model_keys = (make_model_tuple(m) for m in models)
  File "/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/django/db/models/utils.py", line 23, in make_model_tuple
    "must be of the form 'app_label.ModelName'." % model
ValueError: Invalid model reference 'x.qiyun_admin_productconfig_cloudserver.HostType

Mas, meu caminho de modelo HostType é este:
x.qiyun_admin_productconfig_cloudserver.models.HostType.

O retorno menos o.models iniciar. Não sei porque.

PAY ATTENTION, o serializador e as visualizações (visualização do serializador) estão sob oapi diretório.

e as configurações:

...
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
PARENT_DIR = os.path.abspath(os.path.join(BASE_DIR, os.pardir))


sys.path.insert(0, BASE_DIR)
sys.path.insert(0, os.path.join(PARENT_DIR,'x'))
sys.path.insert(0, os.path.join(PARENT_DIR,'x'))
sys.path.insert(0, os.path.join(PARENT_DIR,'x'))
...

INSTALLED_APPS = [
    'django.contrib.admin',
     ....
    'x.qiyun_admin_useradminmanage',  #  
    'x.qiyun_admin_usergroups',  #  

    'x.qiyun_admin_productconfig_common', #  
    'x.qiyun_admin_productconfig_cloudserver',  #  

    'x.qiyun_admin_financialmanage_ordermanage', # 
    'x.qiyun_admin_financialmanage_financialmanage', 

EDITAR

Eu tenho dois modelos (AvailableArea, AddressRegion) nos mesmos models.py (x.qiyun_admin_productconfig_cloudserver.):

class AvailableArea(models.Model):
    name = models.CharField(max_length=8)
    addressregion = models.ForeignKey(AddressRegion, default=1, related_name='availableareas', on_delete=models.CASCADE)

    def __str__(self):
        return self.name
    def __unicode__(self):
        return self.name

class AddressRegion(models.Model):
    name = models.CharField(max_length=8)

    def __str__(self):
        return self.name
    def __unicode__(self):
        return self.name

Você vê, eu ainda deveria especificar oaddressregion = models.ForeignKey('qiyun_admin_productconfig_cloudserver.AddressRegion',...)?

E se outros modelos, se tiver ForeignKey, se referirem aAddressRegion, Eu também o importei.