Marshmallow Deserialize Nested Schema

Python Help
1

Hi everyone, I am trying to find a way to deserialize a json object using Marshmallow.

I have a schema that is like this

class CustomerDTO(BaseDTO):
    first_name: str = fields.Str(required=True)
    last_name: str = fields.Str(required=True)
    address: AddressDTO = fields.Nested(AddressDTOSchema, required=True)

class CustomerDTOSchema(Schema, CustomerDTO)
    pass

class AddressDTO(BaseDTO):
    street_name_one: str = fields.Str(required=True)
    street_name_two: str = fields.Str(required=False)
    state: str = fields.Str(required=True)
    zip: str = fields.Str(required=True)
class AddressDTOSchema(Schema, AddressDTO)
    pass


def GetJson():
    customer_dto_data = request.get_json()
    customer_dto_schema = CustomerDTOSchema().load(customer_dto_data)
    customer_dto = CustomerDTO(**customer_dto_schema)
   print(customer_dto) # prints out the entire object in dictionary format
   print(customer_dto.first_name) # works great
   print(customer_dto.address.street_name_one) # I get -> AttriuteError: 'dict' object has no attribute 'street_name_one'
 print(customer_dto.address) # prints out the values for address just fine.

Is there a way for me to help the object be deserialized correctly?

2

Hi! Unfortunately, this seems to be an issue specific to Mashmellow, so unless someone here happens to be familiar with it, you are probably better off reaching out to a marshmellow-specific support channel instead. Best of luck!

3

I don’t have full experience with vanilla Marshmallow, but it doesn’t look like the constructor of BaseDTO can handle nested models. I don’t know what BaseDTO even is.

In vanilla Marshmallow, you have to declare deserialisation using the post_load decorator on methods of all of your schema classes: see Quickstart — marshmallow 3.14.1 documentation

I do have experience with marshmallow-dataclasses, which reduces boilerplate and improves the typing experience. You’ll probably want Python 3.10 with keyword-only fields though

1 Like