title: Django rest framework abstract model/serializer
body: <p>I have a class Contact and 2 subclasses: Person, Company.</p>
  
  <p>In my API, I'm trying to make a list with both companies and persons with the specialized fields filled, but I'm getting only the Contact's fields with this code.</p>
  
  <pre><code>class Contact(EntityBase):
      #base contact fields
  
  class Company(Contact):
      #Company fields
  
  class Person(Contact):
      #person fields
  </code></pre>
  
  <p>Serializers:</p>
  
  <pre><code>class PersonSerializer(serializers.ModelSerializer):
      #all fields (base and specialized) specified
  
  
  class CompanySerializer(serializers.ModelSerializer):
      #all fields (base and specialized) specified
  
  class ContactSerializer(serializers.ModelSerializer):
      class Meta:
          model = Contact
  
      def to_native(self, obj):
          #polymorphic serialzer
          if isinstance(obj, Person):
              return PersonSerializer(obj, context=self.context).to_native(obj)
          if isinstance(obj, Person):
              return PersonSerializer(obj, context=self.context).to_native(obj)
  </code></pre>
  
  <p>and View:</p>
  
  <pre><code>class ContactViewset(viewsets.ModelViewSet):
      queryset = Contact.objects.all()
      serializer_class = ContactSerializer
  </code></pre>
  
  <p>With all this code, I get everything ok, but not the specialized fields. How can I do that? Is it possible?</p>