"Unknown field" after updating to 3.5.0 marshmallow

Question

Updated dependency in my project

Before

marshmallow-sqlalchemy==0.17.0
marshmallow==3.0.0b6

After

marshmallow-sqlalchemy==0.21.0
marshmallow==3.5.0

I have such a model (simplified):

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class MyModel(Base):
    __tablename__ = 'my_model'

    id = Column(BigInteger, primary_key=True)
    field_name = Column(String)
    password = Column(String)

And schema:

from marshmallow import fields
from marshmallow_sqlalchemy import (
    ModelSchema,
    field_for,
)
class RegistrarSchema(ModelSchema):
    class Meta:
        model = MyModel

    other_field_name = fields.Function(lambda obj: obj.field_name)
    field_name = field_for(MyModel, 'field_name', load_from='other_field_name')

    password = fields.Method("get_password")

    def get_password(self, obj):
        return decrypt_password(obj)

    def load(self, data, session=None, instance=None, transient=False, *args, **kwargs):
        if 'password' in data:
            password = data['password']
            instance = encrypt_password(password, instance)
        return super(ModelSchema, self).load(
            data, *args, session=session, instance=instance,
            transient=transient, **kwargs
        )

And using this code i could call

RegistrarSchema.load(data={'other_field_name': 'my_value'}, instance=instance, session=session)

and this value would be saved to field_name in my database.

After update i lost this functional - now i get

File "myfile.py", line 116, in load
    transient=transient, **kwargs
  File "/usr/local/lib/python3.7/dist-packages/marshmallow_sqlalchemy/schema.py", line 214, in load
    return super().load(data, **kwargs)
  File "/usr/local/lib/python3.7/dist-packages/marshmallow/schema.py", line 723, in load
    data, many=many, partial=partial, unknown=unknown, postprocess=True
  File "/usr/local/lib/python3.7/dist-packages/marshmallow/schema.py", line 904, in _do_load
    raise exc
marshmallow.exceptions.ValidationError: {'other_field_name': ['Unknown field.']}

And exaclty same error when updating password -

RegistrarSchema.load(data={'password': 'my_value'}, instance=instance, session=session)

I didnt write this code myself and cant contact developer who did it.

As i get it the goal for the first case is to give ability to write in both way -data={'my_field': 'value'} and data={'other_field_name': 'value'}. First scenario still working on new version, but the second not.

And in case with password - goal is to make serialization/deserialization more complex with encrypting/decrypting data.

I read update notes but was not able to find anyting specific to this issue, can someone help?

https://marshmallow.readthedocs.io/en/stable/upgrading.html#schemas-raise-validationerror-when-deserializing-data-with-unknown-keys — Jérôme, Mar 27 '20 at 13:32

score 11 · Answer 1 · edited Jul 05 '22 at 11:48

In v3., marshmallow changed the default behavior from EXCLUDE to RAISE https://marshmallow.readthedocs.io/en/stable/quickstart.html#handling-unknown-fields.

You can revert to the old behavior by specifying unknown in the class Meta of your Schema:

from marshmallow import EXCLUDE
class UserSchema(Schema):
    class Meta:
        unknown = EXCLUDE

at instantiation time,

schema = UserSchema(unknown=EXCLUDE)

or when calling load.

UserSchema().load(data, unknown=EXCLUDE)

The unknown option value set in load will override the value applied at instantiation time, which itself will override the value defined in the class Meta.

"Unknown field" after updating to 3.5.0 marshmallow

1 Answers1