Marshmallow: Wrong field name in errors dict when using @validates on load_from/data_key aliased field

[m-novikov]

I am using marshmallow 2.14.
Given following code:

from marshmallow import Schema, fields, ValidationError, validates

class Broken(Schema):
    f = fields.String(required=True, load_from='f-name')
    f2 = fields.String(required=True, load_from='f2-name')

    @validates('f')
    def validate_string(self, data):
        raise ValidationError('nope')

_, err = Broken().load({'f': 'hello', 'f2': None}) # does not throw validation error
print(err)

I get following output:

{'f': ['nope'], 'f2-name': ['Field may not be null.']}

But I would expect to end up with:

{'f-name': ['nope'], 'f2-name': ['Field may not be null.']}

There is seems to be no way to override this behavior.
I suppose it should use load_from field on load and dump_to on dump for errors.

[lafrech]

In marshmallow 3, this changed a bit.

• load_from is merged with dump_to into data_key
• only data_key is checked when deserializing
• also, all Schemas are strict

Your example would write:

from marshmallow import Schema, fields, ValidationError, validates

class Broken(Schema):
    f = fields.String(required=True, data_key='f-name')
    f2 = fields.String(required=True, data_key='f2-name')

    @validates('f')
    def validate_string(self, data):
        raise ValidationError('nope')


try:
    Broken().load({'f-name': 'hello', 'f2': None})
except ValidationError as exc:
    print(exc)

And there is indeed an issue because when using @validates, the wrong field name is used ('f' instead of 'f-name':

{'f2-name': ['Field may not be null.'], 'f': ['nope']}

[lafrech]

This can be fixed by modifying those two lines:

https://github.com/marshmallow-code/marshmallow/blob/2.x-line/marshmallow/schema.py#L889
https://github.com/marshmallow-code/marshmallow/blob/2.x-line/marshmallow/schema.py#L904

  -                          field_name=field_name,
  +                          field_name=field_obj.load_from or field_name,

And likewise with data_key for the 3.x branch.

@m-novikov, would you be willing to send a PR with a test for both cases (many and not many)?

Please PR against 2.x branch. We can take care of porting to 3.x.

Thanks.

[m-novikov]

Yes, no problem. Will do it this week.