🐛 Recurse into dataclass when encoding

[ConorStevenson]

Context:
PR #3576 added support for dataclasses as response objects.

Problem:
json_encoder doesn't recurse into dataclasses as it does for pydantic models, dictionaries, and other collections. Custom encoders aren't applied to attributes on dataclasses.

Solution:
Recurse into dataclasses when encoding. Also change dataclass tests to use dataclasses rather than pydantic models.

Example:

from datetime import datetime
from fastapi import FastAPI
import dataclasses
import pydantic

app = FastAPI()

@pydantic.dataclasses.dataclass
class PydanticDataclass:
    timestamp: datetime = datetime.now()

@dataclasses.dataclass
class ClassicDataclass:
    timestamp: datetime = datetime.now()

@app.get("/pydantic", response_model=PydanticDataclass)
async def pydantic_dataclass():
    return PydanticDataclass()


@app.get("/classic", response_model=ClassicDataclass)
async def classic_dataclass():
    return ClassicDataclass()

$ curl localhost:8000/pydantic
-> {"timestamp":"2022-01-24T20:51:42.316967"}
$ curl localhost:8000/classic
-> TypeError: Object of type datetime is not JSON serializable

[himbeles]

See also my existing (nearly identical) PR #3607 and issue #3608 from last year. No response until now unfortunately.

[don4of4]

Looks good -- encountered this issue in our projects as well.

[himbeles]

Shouldn’t the keyword arguments of jsonable_encoder also be passed on into the recursion? See also #3607.

[ConorStevenson]

Shouldn’t the keyword arguments of jsonable_encoder also be passed on into the recursion? See also #3607.

Yep, updated it now. Sorry to have duplicated your existing PR!

[himbeles]

No problem, just hope it gets merged :)

[himbeles]

@don4of4 Thanks for the review. Do you see any chances, that this PR will be merged in the near future?

[himbeles]

My PR #3607 got merged. I think you can close this one now! 🚀

[tiangolo]

Thanks for the effort @ConorStevenson! ☕

It seems this was solved by #3607, right? Given that, I'll close this one.

But if you feel there's something else that needs to be done, feel free to create a new PR.

Thanks! 😄