[FIXED] Marshmallow Validation Error of Unknown field for Dict and List of Dict in POST payload

Issue

This is a POST payload body received in backend for store and order generated in a test frontend application that includes 2 keys with objects List and a Object

{
    "orderedItems": [
    {
        "id": 1,
        "name": "Asado",
        "amount": 2,
        "price": 15.99
    },
    {
        "id": 3,
        "name": "Sushi",
        "amount": 1,
        "price": 22.99
    },
    {
        "id": 6,
        "name": "Green Bowl",
        "amount": 1,
        "price": 18.99
    }
],
  "user": {
        "city": "Guatemala",
        "email": "[email protected]",
        "name": "danny"
    }
}

Once is received I tried to validate in Marshmallow with OrderSchema nested Schema

from marshmallow import validate, validates, validates_schema, \
    ValidationError, post_dump, validates
from api import ma


class MealsOrderSchema(ma.Schema):
  id= ma.Integer(required=True)
  amount= ma.Integer(required=True)
  price= ma.Float()
  name= ma.String()


class UserDataSchema(ma.Schema):
  name= ma.String(required=True)
  email= ma.String(required=True, validate=[validate.Email()])
  city= ma.String()


class OrderSchema(ma.Schema):
  orderedItems= ma.Nested(MealsOrderSchema(many=True))
  userData= ma.Nested(UserDataSchema)

Validation is not pass for Object List or object neither, I checked in similar question or other blogs for workaround

{
    "code": 400,
    "description": "The server found one or more errors in the information that you sent.",
    "errors": {
        "json": {
            "orderedItems": [
                "Unknown field."
            ],
            "user": [
                "Unknown field."
            ]
        }
    },
    "message": "Validation Error"
}

Appreciate your hints, thanks

Solution

If you need to manage a list of objects you must use the List class. While if the json field name is different from the property name in python, you have to specify which field to load via the attribute parameter

from marshmallow import Schema, fields

class OrderSchema(Schema):
  orderedItems: fields.List(fields.Nested(MealsOrderSchema))
  userData: fields.Nested(UserDataSchema, attribute='user')

Answered By - Matteo Pasini