Add a `many` option to `DataClassJsonMixin.from_json`

[lidatong]

Add a `many` option to `DataClassJsonMixin.from_json`

[lidatong]

Hi, thanks for raising this use case!

This is addressed in two ways in the latest release:

1. .schema will now generate defaults. If your dataclass field uses default or default_factory, @dataclass_json will now supply a corresponding field default to the generated marshmallow schema (so if the key is missing in the JSON, the default will be filled for that key).
2. .schema has an infer_missing parameter. If your dataclass field is Optional without a default, calling .schema(infer_missing=True) will fill None when the key is missing.

I think the 2nd should cover your use case, but you can also solve it by attaching a default to your dataclass e.g.

class Example:
    x: int = 0