Optional string field causing TypeError during validation.

[pyarun]

Probably I am not using dataclass properly as this looks like a simple issue, here is my code

@dataclasses.dataclass
class OrderItem(TypedJsonMixin):
    product_id: typing.Union[uuid.UUID, str]
    unit_price: float
    quantity: int
    product_type: str
    discount: float
    status: typing.Optional[str] = ""
    description: typing.Optional[str] = None
    message: typing.Optional[str] = None  # Order status message.

class ItemSerializer(DataclassSerializer):
    event = serializers.SerializerMethodField()
    product_id = serializers.UUIDField(required=True)

    class Meta:
        dataclass = OrderItem
        # fields = "__all__"
        read_only_fields = ("description", "message")
        extra_kwargs = {
            # "product_id": {"max_length": 36, "required": True},
            "product_type": {"required": True},
            "status": {"default": "in-cart"},
        }

Now while creating an instance of ItemSerializer, I am not passing description and message.

data = {
          "product_id": "a503e2e0-ce0e-4556-bb58-08d4f99f199e",
          "product_type": "public-event",
          "unit_price": 500,
          "quantity": 1,
          "discount": 10
        }
s = ItemSerializer(data=data)
s.is_valid()

I am getting the following error, as empty_values is rest_framework.fields.empty

Error

serializer.is_valid(raise_exception=True)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 234, in is_valid
    self._validated_data = self.run_validation(self.initial_data)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 433, in run_validation
    value = self.to_internal_value(data)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 490, in to_internal_value
    validated_value = field.run_validation(primitive_value)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 621, in run_validation
    value = self.to_internal_value(data)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 657, in to_internal_value
    validated = self.child.run_validation(item)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework/serializers.py", line 433, in run_validation
    value = self.to_internal_value(data)
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/rest_framework_dataclasses/serializers.py", line 531, in to_internal_value
    instance = dataclass_type(**native_values, **empty_values)
  File "<string>", line 11, in __init__
  File "/Users/arun/.local/share/virtualenvs/djZipDate-ChKVyfQ3/lib/python3.8/site-packages/typed_json_dataclass/typed_json_dataclass.py", line 67, in __post_init__
    raise TypeError((f'{class_name}.{field_name} was '
TypeError: OrderItem.description was defined to be any of: (<class 'str'>, <class 'NoneType'>) but was found to be <class 'type'> instead

I read some existing issues about optional fields, but do not see a solution.

[oxan]

You shouldn't pass the data you want to deserialize as keyword arguments to the serializer, but as the data parameter.

[oxan]

The error you get seems to be because TypedJsonMixin does type validation on the values of a dataclass instance, and that conflicts with our handling of non-supplied values. I'd suggest to ditch the TypedJsonMixin, since the serializer does validation already.

[pyarun]

You shouldn't pass the data you want to deserialize as keyword arguments to the serializer, but as the data parameter.

Changed the example code according to feedback. It was a mistake while writing code sample here. Sorry about it!

I went on to remove TypedJsonMixin, and this error is resolved. But TypedJsonMixin is giving 2 useful methods to_json and to_dict which are used in many places!

After serializer validation, we are getting OrderItem instance in def create(self, validated_data) method, which is awesome. But after all processing when i have to save this data in django.contrib.postgres.fields.jsonb.JSONField i need to convert OrderItem instance to a dict where to_dict is very useful.

Still I replaced TypedJsonMixin with https://pypi.org/project/dataclasses-json/ which is a subset of TypedJson and do not deal with type conversion and validation.

order_item.to_json()    # order_item is OrderItem instance

We still have problem as OrderItem.description has value of rest_framework.fields.empty which cannot be converted to JSON and fails with

TypeError: Object of type type is not JSON serializable

[oxan]

I went on to remove TypedJsonMixin, and this error is resolved. But TypedJsonMixin is giving 2 useful methods to_json and to_dict which are used in many places!

FYI Python has a native method to convert dataclasses to dicts: https://docs.python.org/3/library/dataclasses.html#dataclasses.asdict.

We still have problem as OrderItem.description has value of rest_framework.fields.empty which cannot be converted to JSON and fails with

TypeError: Object of type type is not JSON serializable

You can call _strip_empty_sentinels() to get rid of those empty values. However, as that method is still internal (for now) and actually has a different signature in master than in v0.8, it's probably a better idea to do a super-call to the create() or update() methods:

   def create(self, validated_data):
      order_item = super(MyCustomSerializerName, self).create(validated_data)
      order_item.to_json()

[oxan]

I don't think there's anything actionable remaining here, so I'll close this issue for now.