Is it possible to have multiple body schemas?

[jonDel]

Description

In a Response, according to the documentation, I can have a Union of multiple pydantic models as the response of an endpoint operation. That works fine. However, it seems that there is no way to use a similar approach when receiving input in a a body. My problem: I have an endpoint, and this endpoint could receive any of 4 different models as valid input in the body. I tried to define a Union, and it breaks the fastapi schema generation; I tried to use Any, from pydantic, and fastapi treats the input as a query operation instead of a body operation (the same happens if I don't use any model at all)

Consider Foobar, Model1 and Model2 as pydantic classes.

The following breaks schema generation:

@router.post("/{foobar}")
def post_foobar(foobar: Foobar, bar: Union[Model1, Model2], response: Response):

The following makes fastapi understand bar as a query:

@router.post("/{foobar}")
def post_foobar(foobar: Foobar, bar: Any, response: Response):

The following makes fastapi understand bar as a query either:

@router.post("/{foobar}")
def post_foobar(foobar: Foobar, bar, response: Response):

Is there a way to fix this behavior? Or simply force fastapi to understand "bar" as body and NOT a query parameter?

[inikolaev]

I'm also interested in support of union types in requests.

In my use-case a model has an attribute type, which could be used to figure out which class to instantiate, e.g.:

class Bicycle(BaseModel):
  # attributes specific for bicycle here
  type: str = 'bicycle'

class Car(BaseModel):
  # attributes specific for car here
  type: str = 'car'

class MyRequest(BaseModel):
  vehicle: Union[Bicycle, Car]

In there example above I would like vehicle to an instance of the Car or Bicycle, depending on the value of type attribute received in JSON:

{
  "vehicle": {
    "type": "bicycle",
    "break_type": "hydraulic"
  }
}

[inikolaev]

As I understand it depends on pydantic and I found the following ticket there: pydantic/pydantic#619

[tiangolo]

Thanks for the discussion here @inikolaev .

@jonDel maybe it was a bug at some point and it was fixed in recent versions, because this seems to work:

from fastapi import FastAPI
from typing import Union
from pydantic import BaseModel


class User(BaseModel):
    name: str


class Item(BaseModel):
    size: int
    price: float


app = FastAPI()


@app.post("/multi/")
def process_things(body: Union[User, Item]):
    return body

Still, if you want to have single fields (Any, str, etc) as bodies, check the docs: https://fastapi.tiangolo.com/tutorial/body-fields/

[github-actions]

Assuming the original issue was solved, it will be automatically closed now. But feel free to add more comments or create new issues.

[mcauto]

Thanks for the discussion here @inikolaev .

@jonDel maybe it was a bug at some point and it was fixed in recent versions, because this seems to work:

from fastapi import FastAPI
from typing import Union
from pydantic import BaseModel


class User(BaseModel):
    name: str


class Item(BaseModel):
    size: int
    price: float


app = FastAPI()


@app.post("/multi/")
def process_things(body: Union[User, Item]):
    return body

Still, if you want to have single fields (Any, str, etc) as bodies, check the docs: https://fastapi.tiangolo.com/tutorial/body-fields/

It's works!

but sample request body is empty in swagger

How to set default request body?

[phy25]

@mcauto See #1083.

[ritikjain51]

I have tried the approach. Dynamic schema detection is not happening here.

The current approach is working with basic datatypes like int, float and all but user-defined structures or pydantic models not working. It is considering the object in basic datatype like dict or list.

Thanks in advance

[jammymalina]

I have tried the approach. Dynamic schema detection is not happening here.

The current approach is working with basic datatypes like int, float and all but user-defined structures or pydantic models not working. It is considering the object in basic datatype like dict or list.

Thanks in advance

I am facing the same issue. Is there already a github issue for this open?

[JarroVGIT]

What is the issue then? Because the solution given above works with regard the original issue.

[jammymalina]

I am getting 422 Unprocessable Entity error. Strangely it works fine in the unit test. Let me check it again though, if I don't get back to you then it works fine.

EDIT: Sorry for the created confusion, it seems the input data changed a little - the body was not passing validation. Everything is working as expected once I updated the schema.