title: What is the read/write equivalent of serializers.StringRelatedField?
body: <p>In Django Rest Framework 3, I want to return the unicode value of a pk relationship, the way you can using a serializer.StringRelatedField, but I need the value to be writable, too. StringRelatedField is read only.</p>
  
  <p>I don't care if the API accepts the pk, or the string value, on the PUT (though accepting the string would be nifty, and would save me grabbing all the pks!). The API just needs to return the unicode string value on the GET.</p>
  
  <p>I'm thinking PrimaryKeyRelatedField might be the way to go, but what does the query look like?</p>
  
  <p>For instance, if the model I want is "Model", and I want Model.name to be serialized, what does this command look like:</p>
  
  <pre><code>name = serializers.PrimaryKeyRelatedField(queryset=Model.objects.get(pk=????))
  </code></pre>
  
  <p>I'm struggling because I don't know how to get the pk from the serializer object in order to query the related model ...</p>
  
  <p>That's presuming PrimaryKeyRelatedField is what I need, of course. Which may be totally wrong.</p>
  
  <p>Thanks</p>
  
  <p>John</p>
  
  <p>Here are example models as requested, slightly changed for clarity:</p>
  
  <pre><code>class CarModel(models.Model):
    name = models.CharField(max_length=100,unique=True)
  
    def __str__(self):
      return self.name
  
  
  class Car(models.Model):
    name = models.CharField(max_length=100)
    make = models.ForeignKey(CarMake)
    car_model = models.ForeignKey(CarModel)
  
  class CarSerializer(serializers.ModelSerializer):
     car_model = serializers.StringRelatedField() //like this, but read/write
  
     class Meta:
     model = Car
  </code></pre>
  
  <p>In this example I'm serializing Car, trying to return a string value of CarModel that can be updated with a select dropdown in a form.
  If I use different serializers, one for POST that expects the PK and one for everything else that returns the string, the select directive in the form gets very messy.</p>
  
  <p>So, ideally, I just want to be able to POST the string value, and have the API complete the lookup and save the string as a PK. </p>