python - django object havn't pk but have id -

i have problem objects in django.
project using multiply databases. when create object using

obj, _created = self.model.objects.using('default').get_or_create(pk=1) 

obj don't have pk have id

ipdb> obj.pk ipdb> obj.id 1
why happened?

first answers: what's difference between model.id , model.pk in django? django queries - id vs pk

and doc of 'get_or_create': https://docs.djangoproject.com/en/1.9/ref/models/querysets/#get-or-create

the object has 'pk' when recovered 'bd'. object created, check variable '_created', specifies whether new object created or recovered 'bd'.