django-rest-framework - trying to set required=False flag on nested 1-to-M?

django-rest-framework - trying to set required=False flag on nested 1-to-M?

I'm having some issue with django-rest-framework, and nested objects.
I have a Cart object, as well as CartItem, which links back to a Cart:
class Cart(models.Model):
customer = models.ForeignKey(Customer)
date_created = models.DateTimeField(auto_now_add=True)
date_modified = models.DateTimeField(auto_now=True)
class CartItem(models.Model):
cart = models.ForeignKey(Cart, related_name='cartitems')
product = models.ForeignKey(Product, help_text='Product in a cart')
quantity = models.PositiveIntegerField(default=1, help_text='Quantity
of this product.')
date_added = models.DateTimeField(auto_now_add=True, help_text='Date
that this product was added to the cart.')
I've created serializers for both:
class CartItemSerializer(serializers.ModelSerializer):
product = serializers.HyperlinkedRelatedField(view_name='product-detail')
class Meta:
model = CartItem
class CartSerializer(serializers.ModelSerializer):
customer =
serializers.HyperlinkedRelatedField(view_name='customer-detail')
cartitems = CartItemSerializer(required=False)
total_price = serializers.CharField(source='total_price', read_only=True)
shipping_cost = serializers.CharField(source='shipping_cost',
read_only=True)
class Meta:
model = Cart
fields = ('id', 'customer', 'date_created', 'date_modified',
'cartitems', 'total_price', 'shipping_cost')
However, whenever I try to POST to create a new cart, I get an error,
assumedly when it tries to set the non-existent CartItem:
TypeError at /api/v1/carts/
add() argument after * must be a sequence, not NoneType
However, a Cart isn't required to actually have CartItems.
Is there any way to get DRF to respect the required=False flag I get on
Cart.cartitems?
Cheers, Victor