title: DRF foreign primary key that auto increments with nested serializers for cascade insert
body: <p>I want to insert a Conversation model that has a child class to Message model.<br>
  I also want it to use a single Viewset method for the saving.<br>
  The Message has a foreign key to the primary key of Conversation.</p>
  
  <p>I'm looking for something similar to the java + spring class implementation wherein the Parent references the Child class.<br>
  The Parent and Child have an auto_increment annotation. Spring JPA save is called and the insert is cascaded.</p>
  
  <p>Parent Class:</p>
  
  <pre><code>int id;
  Child reference;
  </code></pre>
  
  <p>Child Class:</p>
  
  <pre><code>int child_id;
  int parent_id;
  </code></pre>
  
  <p>Service Method:</p>
  
  <pre><code>parent.setReference(child);
  jpa.save(parent); // both parent and child is inserted
  </code></pre>
  
  <p>Is there something like this for Django Rest Framework? Or Django Framework?</p>
  
  <p>json:</p>
  
  <pre><code>{
    "model": "conversation",
    "id": auto_increment,
    "title": "chat",
    "message": {
      "model": "message",
      "conversation_id": value from id in conversation model,
      "message": "hi"
    }
  }
  </code></pre>