[Answer]-Django create_or_update(), unique_together, unique, and primary

Django automatically sets a primary key field called id unless you specify one yourself. So your Car model will already have an id field. It’s on the base model class that your model inherits.

In your example, you haven’t specified the defaults argument of the get_or_create() method, so Django will only attempt to retrieve an object with the values you’ve passed in via a get call: https://docs.djangoproject.com/en/1.7/ref/models/querysets/#django.db.models.query.QuerySet.get_or_create

unique constraints can be specified on a field regardless if it’s an AutoField or not. See: https://docs.djangoproject.com/en/1.7/ref/models/fields/#unique for more specific information.