Enum parameters are ignored when loading a schema

[therice]

Enum parameters are ignored when loading a schema

[otonnesen]

I think the issue is in this line:

    version : Version = field_for_schema(Version, metadata={'by_value' : True})

Fields are intended to be passed as annotations for the dataclass's fields, not as defaults for them. marshmallow-dataclass sees version : Version and makes a field called "version" and binds to it a marshmallow field constructed from the Version Enum (i.e. no custom metadata), then sets the default for that marshmallow field to field_for_schema(Version, metadata={'by_value' : True}) . We can see this behaviour by not passing any value for version when loading:

>>> @dataclass
... class VersionContainer:
...     version : Version = field_for_schema(Version, metadata={'by_value' : True})
...
>>> class_schema(VersionContainer)().load({})
VersionContainer(version=<fields.Enum(dump_default=<marshmallow.missing>, attribute=None, validate=None, required=True, load_only=False, dump_only=False, load_default=<marshmallow.missing>, allow_none=False, error_messages={'required': 'Missing data for required field.', 'null': 'Field may not be null.', 'validator_failed': 'Invalid value.', 'unknown': 'Must be one of: {choices}.'})>)

The workaround you posted is just the standard/intended way to pass in extra field metadata when using this library (see https://github.com/lovasoa/marshmallow_dataclass#customizing-generated-fields). Another option if you wish to avoid this field syntax could be to use marshmallow_dataclass.NewType instead, eg:

>>> VersionField = marshmallow_dataclass.NewType("Version", Version, field=marshmallow.fields.Enum, enum=Version, by_value=True)
>>> @dataclass
... class VersionContainer:
...     version: VersionField
...
>>> class_schema(VersionContainer)().load({"version": "foo/v1"})
VersionContainer(version=<Version.v1: 'foo/v1'>)

Hope that helps! Let me know if I misunderstood the problem.

[dairiki]

Test case which demonstrates the problem

...
@dataclass
class VersionContainer:
    version : Version = field_for_schema(Version, metadata={'by_value' : True})

This is incorrect usage of field_for_schema. (In fact direct use of field_for_schema is not documented.)

Workaround appears to declare the field using dataclasses directly instead of marshmallow_dataclass

from dataclasses import dataclass, field
...
@dataclass
class VersionContainer:
    version : Version = field(default=None, metadata={'by_value' : True})

This is not so much a workaround, as closer to correct usage.

Even more correct, assuming that you do not want to specify a default value for VersionContainer.version would be:

@dataclass
class VersionContainer:
    version : Version = field(metadata={'by_value' : True})

I don't think this is a bug. (The immediately preceding example appears to work fine for me.)
Closing. Feel free to reopen if the situation warrants.

[therice]

Workaround appears to declare the field using dataclasses directly instead of marshmallow_dataclass

...
from dataclasses import dataclass, field
...
@dataclass
class VersionContainer:
    version : Version = field(default=None, metadata={'by_value' : True})