`to_dict()` fails and ignores `encoder`

[ItayGoren]

Issue

When one of the fields is Dict and its key is a hashable dataclass, calling to_dict() fails with TypeError: unhashable type: 'dict'.

Example code

from dataclasses import dataclass, field
from dataclasses_json import dataclass_json, config
from typing import Dict

@dataclass_json
@dataclass(frozen=True)
class A:
    x: int

@dataclass_json
@dataclass
class B:
    attr: Dict[A, str] = field(
        metadata=config(
            encoder=lambda x: 3,
            decoder=lambda x: {'foo': 'bar'},
        )
    )

print(B({A(3): 'bar'}).to_dict())

The error:

Traceback (most recent call last):
  File "error.py", line 21, in <module>
    print(B({A(3): 'bar'}).to_dict())
  File "/usr/local/opt/[email protected]/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/dataclasses_json/api.py", line 86, in to_dict
    return _asdict(self, encode_json=encode_json)
  File "/usr/local/opt/[email protected]/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/dataclasses_json/core.py", line 323, in _asdict
    value = _asdict(getattr(obj, field.name), encode_json=encode_json)
  File "/usr/local/opt/[email protected]/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/dataclasses_json/core.py", line 331, in _asdict
    return dict((_asdict(k, encode_json=encode_json),
TypeError: unhashable type: 'dict'

Expected behavior

As you can see, I specified how to encode and decode the field using encoder and decoder. Hence, dataclasses-json shouldn't call its inner implementation. As you can see in the implementation, the following is called:

    elif isinstance(obj, Mapping):
        return dict((_asdict(k, encode_json=encode_json),
                     _asdict(v, encode_json=encode_json)) for k, v in
                    obj.items())

Specifically what fails is _asdict(k, ...). Yet, this code shouldn't be called because encoder is specified.

[sergei-mironov]

I also hit this problem, even without special encoders/decoders

[matt035343]

I tested this in Python 3.8 / dataclasses-json newest version on master, and this code runs just fine. Closing issue, but if it reappears, please reopen this issue with more details.