Marshmallow: Question: How can I pass the context in a nested field of a structured dict?

[RosanneZe]

I noticed that if you use a nested field for values in a structured Dict, the context is not automatically given to the nested schema. Is there a way to pass it the context?

Example:

class Inner(Schema):
    foo = fields.String()

    @validates('foo')
    def validate_foo(self, value):
        if 'foo_context' not in self.context:
            raise ValidationError('no context!')


class Outer(Schema):
    bar = fields.Dict(values=fields.Nested(Inner))

# gives no error:
Inner(context={'foo_context': 'foo'}).load({'foo': 'some foo'})
# gives 'no context!' error:
Outer(context={'foo_context': 'foo'}).load({'bar': { 'key': {'foo': 'some foo'}}})

[lafrech]

I'm not familiar with the "context" feature, but from a quick glance, this looks like a bug.

[sloria]

Yeah, AFAIK, Dict does not pass down context to it's inner fields, like Nested does.

[deckar01]

Does List pass the context correctly?

[lafrech]

I'm afraid it does not.

[sloria]

It looks like List works as expected. The following test passes on 2.x-line:

    def test_nested_list_fields_inherit_context(self):
        class InnerSchema(Schema):
            foo = fields.Field()

            @validates('foo')
            def validate_foo(self, value):
                if 'foo_context' not in self.context:
                    raise ValidationError('Missing context')

        class OuterSchema(Schema):
            bars = fields.List(fields.Nested(InnerSchema()))

        inner = InnerSchema(strict=True)
        inner.context['foo_context'] = 'foo'
        assert inner.load({'foo': 42})

        outer = OuterSchema(strict=True)
        outer.context['foo_context'] = 'foo'
        assert outer.load({'bars': [{'foo': 42}]})

And I verified that the test fails if outer.context['foo_context'] = 'foo' is removed.

[deckar01]

Dict needs to copy the _add_to_schema logic from List to link the "container" to the parent.

[RosanneZe]

Thanks for the quick fix everyone!