Allow None to be used as a valid json value.

[bharel]

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Description

ATM, if you receive a post with the following json: {data: null}

And you have the following definition:

@app.post("/")
def post_data(data: Optional[str] = Body(...)):
  pass

FastAPI will say data was not passed. That's because it internally uses None as a placeholder for non-existing fields, instead of a sentinel value.

I wish to explicitly require null as one of the possible values, and not put a default value of None.

I've attempted to open a PR, but it failed. It looks like the issue is with dependencies.utils.request_body_to_args using None as a default value for value.

Environment

• OS: [e.g. Linux / Windows / macOS]: macOS
• FastAPI Version [e.g. 0.3.0]: 0.58.1
• Python version: 3.8.3

[Kludex]

Well, in your example data is not a json. You're trying to use it as a Query.

You're probably aiming for:

from typing import Optional
from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

class Data(BaseModel):
    data: Optional[str]

@app.post("/")
def post_data(data: Data):
    return data

Which works just fine.

[bharel]

@Kludex Updated example, meant to use it with Body(...). Perhaps it works only in a model and not as a body param?

[Kludex]

I've never tried receiving a string from a Body, not sure what expect from this notation. I'm not sure if doing that makes sense by definition. The way I interpret your code is: you're passing a JSON and then trying to catch it with an Optional[str].

On my example you validate your JSON with Data, using the data field (sorry about the similarity of the class and property names).

[bharel]

I'm passing a json, extracting the data field from the json, validating the data field as Optional[str].

It's all supported and works well, until the data field in the json is set to null. Then the whole world explodes and I'm left crying 😢

[rspadim]

If i’m not wrong “...” means that a value must exists maybe changing body(...) to body(any) should works

[bharel]

If i’m not wrong “...” means that a value must exists maybe changing body(...) to body(any) should works

It exists. None or null is a value. If someone explicitly gave me None, I'd like to accept it as a possible value.
Atm I can only resolve to workarounds such as parsing the json myself...

[rspadim]

Try with Any or Union[Any, None]
I’m not on computer now

[tiangolo]

Thanks for the help here everyone! 👏 🙇

@bharel If you solved the original problem, then you can close this issue ✔️

Otherwise, please make a minimum app that can show how to replicate the problem. Something that can be run directly with Uvicorn. That way me or others can try it and see the problem.

[MatthewScholefield]

@tiangolo Hi, I ran into the same issue. I've adding imports to the author's example to illustrate it:

example.py:

from fastapi import FastAPI, Body
from typing import Optional

app = FastAPI()

@app.post("/")
def post_data(data: Optional[str] = Body(...)):
      pass

Now, start uvicorn:

uvicorn example:app

Finally, test with curl:

$ curl -X POST "http://localhost:8000/" -d '"hello"' -H "Content-Type: application/json"
null
$ curl -X POST "http://localhost:8000/" -d 'null' -H "Content-Type: application/json"
{"detail":[{"loc":["body"],"msg":"field required","type":"value_error.missing"}]}

Expected result (doesn't happen):

$ curl -X POST "http://localhost:8000/" -d 'null' -H "Content-Type: application/json"
null

I would have expected null would not return an error because the value None/null is valid for the Optional[str] type.

[tiangolo]

Hey there! I just tested it out with FastAPI 0.85.1 and it seems to be working as expected 🎉

I think this was probably added in some of the "recent" versions.

Please try again with a recent version, and if it works correctly you can close the issue. 🤓 🍰