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
EDIT:
I took a stab at tracing it through again:
It's calling BaseSerializer.save() in rest_framework/serializers.py with a CartSerializer object.
def save(self, **kwargs):
"""
Save the deserialized object and return it.
"""
if isinstance(self.object, list):
[self.save_object(item, **kwargs) for item in self.object]
if self.object._deleted:
[self.delete_object(item) for item in self.object._deleted]
else:
self.save_object(self.object, **kwargs)
return self.object
It then calls save_object() on the same class:
def save_object(self, obj, **kwargs):
"""
Save the deserialized object and return it.
"""
if getattr(obj, '_nested_forward_relations', None):
# Nested relationships need to be saved before we can save the
# parent instance.
for field_name, sub_object in obj._nested_forward_relations.items():
if sub_object:
self.save_object(sub_object)
setattr(obj, field_name, sub_object)
obj.save(**kwargs)
if getattr(obj, '_m2m_data', None):
for accessor_name, object_list in obj._m2m_data.items():
setattr(obj, accessor_name, object_list)
del(obj._m2m_data)
if getattr(obj, '_related_data', None):
for accessor_name, related in obj._related_data.items():
if isinstance(related, RelationsList):
# Nested reverse fk relationship
for related_item in related:
fk_field = obj._meta.get_field_by_name(accessor_name)[0].field.name
setattr(related_item, fk_field, obj)
self.save_object(related_item)
# Delete any removed objects
if related._deleted:
[self.delete_object(item) for item in related._deleted]
elif isinstance(related, models.Model):
# Nested reverse one-one relationship
fk_field = obj._meta.get_field_by_name(accessor_name)[0].field.name
setattr(related, fk_field, obj)
self.save_object(related)
else:
# Reverse FK or reverse one-one
setattr(obj, accessor_name, related)
del(obj._related_data)
The Cart object has a _related_data field that is set to a dict:
{'cartitems': None}
Hence, on the second-last line, it calls setattr in django/db/models/fields/related.py:
def __set__(self, instance, value):
if instance is None:
raise AttributeError("Manager must be accessed via instance")
manager = self.__get__(instance)
# If the foreign key can support nulls, then completely clear the related set.
# Otherwise, just move the named objects into the set.
if self.related.field.null:
manager.clear()
manager.add(*value)
It's this last liner (manager.add(*value)) that causes the:
TypeError: add() argument after * must be a sequence, not NoneType
