title: django-rest ModelSerializer select fields to display in nested relationship
body: <p>I'm going to reference the django-rest-framework API example on this. Lets say we have two serializers defined as below.</p>
  
  <pre><code>class TrackSerializer(serializers.ModelSerializer):
      class Meta:
          model = Track
          fields = ['order', 'title', 'duration']
  
  class AlbumSerializer(serializers.ModelSerializer):
      tracks = TrackSerializer(many=True, read_only=True)
  
      class Meta:
          model = Album
          fields = ['album_name', 'artist', 'tracks']
  </code></pre>
  
  <p>Now if i do a GET request and retrieve an <code>Album</code> instance, it will return me a response with a list of <code>Track</code> instances inside it where each instance contains all the fields of Track. Is there a way to return only a selected subset of the fields in the <code>Track</code> model? For example to only return the <code>title</code> and <code>duration</code> field to the client but not the 'order' field.</p>