BaseModel with simple __root__ type not allowed in Path and Query params

[ghost]

Describe the bug

I want to extract enums from model schema to separate definition, and the solution is:

from enum import Enum

from pydantic import BaseModel
from devtools import debug

class HelloType(str, Enum):
    World = 'World',
    Friend = 'Friend',

class HelloEnum(BaseModel):
    __root__: HelloType

class Foo(BaseModel):
    bar: HelloEnum

debug(HelloEnum.schema())
debug(Foo.schema())

Output:

./main.py <module>
    HelloEnum.schema(): {
        'title': 'HelloEnum',
        'enum': [
            'World',
            'Friend',
        ],
        'type': 'string',
    } (dict) len=3
./main.py <module>
    Foo.schema(): {
        'title': 'Foo',
        'type': 'object',
        'properties': {
            'bar': {
                '$ref': '#/definitions/HelloEnum',
            },
        },
        'required': ['bar'],
        'definitions': {
            'HelloEnum': {
                'title': 'HelloEnum',
                'enum': [
                    'World',
                    'Friend',
                ],
                'type': 'string',
            },
        },
    } (dict) len=5

But I can't use HelloEnum in Query parameters:

@app.get('/')
async def root(hello_type: HelloEnum = Query(...)):
    return {'message': f'Hello {hello_type}'}

And I get the error:

File "./main.py", line 28, in <module>
    async def root(hello_type: HelloEnum = Query(...)):
  File "<..>/python3.8/site-packages/fastapi/routing.py", line 514, in decorator
    self.add_api_route(
  File "<..>/python3.8/site-packages/fastapi/routing.py", line 453, in add_api_route
    route = route_class(
  File "<..>/python3.8/site-packages/fastapi/routing.py", line 370, in __init__
    self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
  File "<..>/python3.8/site-packages/fastapi/dependencies/utils.py", line 308, in get_dependant
    assert isinstance(
AssertionError: Param: hello_type can only be a request body, using Body(...)

To Reproduce

1. Create a file with:

from enum import Enum

from fastapi import FastAPI, Query
from pydantic import BaseModel

app = FastAPI()


class HelloType(str, Enum):
    World = 'World',
    Friend = 'Friend',


class HelloEnum(BaseModel):
    __root__: HelloType

@app.get('/')
async def root(hello_type: HelloEnum = Query(...)):
    return {'message': f'Hello {hello_type}'}

3. Run app.
4. It trows an exception AssertionError: Param: hello_type can only be a request body, using Body(...).
5. But I expected it to run successfully.

Expected behavior

Run app successfully, and in openapi schema enum extracted in the separate definition.

Environment

• macOS 10.15.4
• FastAPI 0.54.2
• Python 3.8.2

[phy25]

Do you think it's a duplicate of #911?

[ghost]

Partially. In this case, I am trying to extract the enum in the schema definitions. This useful for openapi-generator, otherwise it generates separate enums (e.g. for typescript).

[espdev]

I have a similar issue. And I try to use request body instead but that raises an error too.

For example:

class QueryDict(BaseModel):
    __root__: dict[str, str]
    
    # some validators here
    ...

class Query(BaseModel):
    query: QueryDict

@app.post('/foo')
def foo(query: Query):
    ...

Request:

curl -X POST "http://127.0.0.1:8888/foo" -H  "accept: application/json" -H  "Content-Type: application/json" -d '{"query":{"hello":"world"}}'

In this case I get a validation error:

{
  "detail": [
    {
      "loc": [
        "body",
        "query",
        "__root__"
      ],
      "msg": "field required",
      "type": "value_error.missing"
    }
  ]
}

#911/#1524 does not fix this.

@tiangolo do you have any thoughts on this?

It seems to me this is a pydantic issue.

Query.parse_obj({"query":{"hello":"world"}})

ValidationError: 1 validation error for Query
query -> __root__
  field required (type=value_error.missing)

pydantic/pydantic#2100

Also nested __root__ parse was fixed in pydantic v1.8 but Query still cannot be custom __root__ model in fastapi.

[tiangolo]

Pydantic models are not supported for other things apart from bodies. I want to add a way to support them for query parameters and others, but that's not supported yet.

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.

[github-actions]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.