Deserializing only specific fields from a schema in fields.Nested?

The only parameter for fields.Nested only applies to serialization.

Since you can only pass the schema class or name string to fields.Nested, there is currently no way to limit which fields are deserialized. Schema.__init__() allows use of dump_only and load_only, but these cannot currently be used with fields.Nested.

Is there a way to limit which fields are deserialized from a nested schema?

[sloria]

I believe the desired behavior is already implemented–the only parameter is respected upon deserialization. I’ve verified that @joshfriend 's code example works in both marshmallow 2.13.3 and 3.0.0b1.

from marshmallow import Schema, fields

class IDSchema(Schema):
    id = fields.Integer()

class ChildSchema(IDSchema):
    name = fields.Str(allow_none=False, required=True)

class ParentSchema(Schema):
    # only load the ID of the nested objects
    children = fields.Nested(
        ChildSchema,
        many=True,
        required=True,
        load_only=True,
        only=('id',)
    )

    class Meta:
        strict = True


sch = ParentSchema()
data = sch.load({'children': [{'id': 1, 'name': 'foo'}]}).data
assert data == {'children': [{'id': 1}]}

[joshfriend]

I’m more interested in using only to ignore any extra info the client might send, rather than accepting however many fields the client wants to send. I think partial will already apply to nested schemas if it is given on the parent.