Non-iterable values get passed as [] to @pre_load @validates_schema et al.

With:

class Foo(StrictSchema):
    foo = fields.Str()

parser = FlaskParser()
    
req = Mock()
req.mimetype = 'application/json'
req.get_json = lambda *_, **__: {'foo': 1}  # or any non-iterable

parser.parse(Foo(strict=True, many=True), req=req, locations=('json', ))

@pre_load(pass_original=True) @validate_schema(pass_original=True) get [] as original value, instead of {'foo': 1}.

This makes it impossible to record errors about invalid base type / extra fields.

This happens for any non-iterable non-string non-mapping value.

The code that’s related to this is in get_value() at https://github.com/sloria/webargs/blob/dev/webargs/core.py#L130-L132. Not yet sure what all that processing really does, but could that function return the data as is…?

[lafrech]

Thanks for looking into this.

[tuukkamustonen]

The problem was with many=True. Added that and made @pre_load take pass_many=True:

import marshmallow as ma
from marshmallow import Schema, fields
from webargs.flaskparser import FlaskParser
from unittest.mock import Mock


class Foo(Schema):

    # Both raise
    @ma.pre_load(pass_many=True)
    def test_pre_load(self, data, **kwargs):
        print('@pre_load data:', data)
        return data

    @ma.validates_schema(pass_original=True)
    def test_validates_schema(self, data, original_data, **kwargs):
        print('@validates_schema data:', data)
        print('@validates_schema original_data:', original_data)
        return data

    foo = fields.Str()


parser = FlaskParser()

req = Mock()
req.mimetype = 'application/json'
req.get_data = lambda *_, **__: '{"foo": "1"}'  # or any non-iterable

parser.parse(Foo(many=True), req=req, location='json')

Prints:

@pre_load data: {'foo': '1'}
Traceback (most recent call last):
    ...
packages/marshmallow/schema.py", line 892, in _do_load
    raise exc
marshmallow.exceptions.ValidationError: {'_schema': ['Invalid input type.']}

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
    ...
werkzeug.exceptions.UnprocessableEntity: 422 Unprocessable Entity: The request was well-formed but was unable to be followed due to semantic errors.

So @pre_load works as expected, it now gets the original payload passed in, as should. This didn’t work earlier so it’s now fixed.

@validates_schema never evaluates now, because exception is raised before it. I don’t know if this is how it should work by design, but I guess yes. IIRC, the problem with earlier versions was that they failed to ensure that given payload was actually an array, when many=True was passed in. Now it seems to do that, and error gets risen. I think current logic is good.

So yeah, let’s assume this fixed.