title: Django rest framework complex return info for a single api
body: <p>How to return complex information in a single api under Django rest framework? 
  Assuming I have a model:</p>
  
  <pre><code>class Apple(models.Model):
      color
      size
      shape
  </code></pre>
  
  <p>With a single api: /api/get-apples, I want to return a json like below:</p>
  
  <pre><code>{"red": {"round":[0.1,0.2,0.3],"spigold":[0.3,0.4,0.5]},
  "yellow":{"round":[0.1,0.2,0.4],"spigold":[0.2,0.4,0.5]}}
  </code></pre>
  
  <p>What will be the best way to achieve this?</p>