Partial validation with marshmallow to ingore unknown field

Question

I have searched this as much as I could, read the docs, looked in various posts but i start to believe it is not possible. So I want to have a partial validation schema, for a Flask app, with marshmallow like this

from marshmallow import Schema, fields, validate


class MySchema(Schema):
    product_type = fields.Str(required=True, allow_none=True)

and i want to validate a dictionary and ensure that it has the product_type field. Now this dictionary might have any number of other fields unknown to me but I don't care, I want to partially validate that the product_type exists. For example:

data={"product_type":"consumable","other_field1":67,"other_field2":"info"...} 

this passes no matter what fields are there BUT only if product type is missing it fails. How is this done?

Answer 1

In the marshmallow documentation there is a section "Handling Unknown Fields", which explains how to handle unknown fields. In addition to the standard procedure, which causes a ValidationError, there is also the option to exclude fields or to include and accept them. The following example shows just one way of using it.

from marshmallow import Schema, fields, validate, INCLUDE

class MySchema(Schema):
    class Meta:
        unknown = INCLUDE
    
    product_type = fields.Str(required=True, allow_none=True)