Optional fields in FormModel not working

[D1maD1m0nd]

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Example Code

class FashionSwapFormData(BaseModel):
    PersonImage: Optional[UploadFile] = File(
        default=None
    ),
    PersonUrl: Optional[str] = Form(
        default=None
    ),

    ClothesImage: Optional[UploadFile] = File(
        default=None
    ),
    ClothesUrl: Optional[str]= Form(
        default=None
    ),
#not working
@router_generation.post(
    "/fashion_swap/",
    response_model_exclude_none=True,
)
async def fashion_swap(
        data: Annotated[FashionSwapFormData, Form(media_type="multipart/form-data")],
) 

#working
@router_generation.post(
    "/fashion_swap/",
    response_model_exclude_none=True,
)
async def fashion_swap(
     PersonImage: Optional[UploadFile] = File(
        default=None
    ),
    PersonUrl: Optional[str] = Form(
        default=None
    ),

    ClothesImage: Optional[UploadFile] = File(
        default=None
    ),
    ClothesUrl: Optional[str]= Form(
        default=None
    ),
)

Description

Hello, in the code above I do not take into account opional fields in the form model, but if I specify them in the function in the same way, everything works fine

For unfilled fields I get the following error

{
"detail": [
{
"type": "string_type",
"loc": [
"body",
"PersonUrl"
],
"msg": "Input should be a valid string",
"input": [
{
"embed": null,
"media_type": "application/x-www-form-urlencoded",
"example": null,
"include_in_schema": true,
"openapi_examples": null
}
]
},
{
"type": "value_error",
"loc": [
"body",
"ClothesImage"
],
"msg": "Value error, Expected UploadFile, received: <class 'tuple'>",
"input": [
{
"embed": null,
"media_type": "multipart/form-data",
"example": null,
"include_in_schema": true,
"openapi_examples": null
}
],
"ctx": {
"error": {}
}
}
]
}

Operating System

Windows

Operating System Details

windows 11

FastAPI Version

0.115.6

Pydantic Version

2.10.3

Python Version

3.12.7

Additional Context

No response

[yvallois]

when I copied and pasted your code my ide transformed your model into:

class FashionSwapFormData(BaseModel):
    PersonImage: Optional[UploadFile] = (File(default=None),)
    PersonUrl: Optional[str] = (Form(default=None),)

    ClothesImage: Optional[UploadFile] = (File(default=None),)
    ClothesUrl: Optional[str] = (Form(default=None),)

I had the same error as you

But if you remove the comma

class FashionSwapFormData(BaseModel):
    PersonImage: Optional[UploadFile] = File(default=None)
    PersonUrl: Optional[str] = Form(default=None)
    ClothesImage: Optional[UploadFile] = File(default=None)
    ClothesUrl: Optional[str] = Form(default=None)

every thing works fine