[FEATURE REQUEST] KeyError using Pydantic dataclass as request body parameter

Describe the bug If a user attempts to use the dataclass from Pydantic to decorate the class used in a request body, a KeyError is thrown when loading the OpenAPI docs.

To Reproduce Steps to reproduce the behavior:

1. Create a file with this example:

from fastapi import FastAPI
from pydantic.dataclasses import dataclass


@dataclass()
class Item:
    name: str
    price: float
    description: str = None
    tax: float = None


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):
    return item

1. Start the app server
2. Open the OpenAPI docs in a browser (e.g. http://127.0.0.1:8000/docs)
3. See error in terminal KeyError: <class 'src.main.Item'>

Expected behavior I expect this to work the same as if I had declared my Item class with Pydantic’s BaseModel. Here’s an example that works as expected:

from fastapi import FastAPI
from pydantic import BaseModel


class Item(BaseModel):
    name: str
    price: float
    description: str = None
    tax: float = None


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):
    return item

Environment:

• OS: macOS
• FastAPI Version: 0.42.0
• Python version, get it with: 3.7.3

Additional context I stumbled across this while trying to adapt this example from the docs to use Pydantic.dataclasses instead of Pydantic.BaseModel.

[MatanRubin]

+1 for supporting pydantic dataclasses as request bodies!

[tiangolo]

Thanks for the report and for the discussion everyone!

This is now supported in FastAPI 0.67.0, the new docs are here: https://fastapi.tiangolo.com/advanced/dataclasses/ 🎉