title: Add Serializer on Reverse Relationship - Django Rest Framework
body: <p>I have a <code>Cart</code> model and a <code>CartItem</code> model. The <code>CartItem</code> model has a <code>ForeignKey</code> to the <code>Cart</code> model.</p>
  
  <p>Using Django Rest Framework I have a view where the API user can display the <code>Cart</code>, and obviously then I want to include the <code>CartItem</code> in the respone. </p>
  
  <p>I set up my Serializer like this:</p>
  
  <pre><code>class CartSerializer(serializers.ModelSerializer):
      user = UserSerializer(read_only=True)
      cartitem_set = CartItemSerializer(read_only=True)
      class Meta:
          model = Cart
          depth = 1
          fields = (
              'id', 
              'user', 
              'date_created', 
              'voucher', 
              'carrier', 
              'currency', 
              'cartitem_set', 
          )
  </code></pre>
  
  <p>My problem is the second line, <code>cartitem_set = CartItemSerializer(read_only=True)</code>.</p>
  
  <p>I get AttributeErrors saying <code>'RelatedManager' object has no attribute 'product'</code>.  ('product' is a field in the <code>CartItem</code> model. If I exclude product from the <code>CartItemSerializer</code> I just get a new AttributeError with the next field and so on. No matter if I only leave 1 or all fields in the Serializer, I will get a error.</p>
  
  <p>My guess is that for some reason Django REST Framework does not support adding Serializers to reverse relationships like this. Am I wrong? How should I do this?</p>
  
  <p>PS</p>
  
  <p>The reason why I want to use the <code>CartItemSerializer()</code> is because I want to have control of what is displayed in the response.</p>