old_contents: from .base import BaseModel
  
  
  class Address(BaseModel):
      _as_is_fields = ['city', 'latitude', 'longitude', 'postal_zip', 'street']
      _resource_fields = [('country', 'Country')]
  
      def __repr__(self):
          return '<{0}: {1}, {2}>'.format(
              self.__class__.__name__, self.city, self.country.name)
  
new_contents: from .base import BaseModel
  
  
  class Address(BaseModel):
      _as_is_fields = ['city', 'latitude', 'longitude', 'postal_zip', 'street']
      _resource_fields = [
          ('state', 'State'),
          ('country', 'Country')
      ]
  
      def __repr__(self):
          return '<{0}: {1}, {2}>'.format(
              self.__class__.__name__, self.city, self.country.name)
  
subject: Add State to Address model definition.