Is it possible to mix UploadFile with List of UploadFile in an endpoint?

[guzman109]

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Example Code

@router.post("/upload",status_code=status.HTTP_201_CREATED)
def upload(
   file_a: Annotated[UploadFile, File(description="File A")],
   file_b: Annotated[UploadFile | None, File(description="Optional File B")] = None,
   files_extra: Annotated[list[UploadFile] | None, File(description="Optional Extra Files")] = None
):
 #

Description

I'm trying to write an endpoint that where the first file is mandatory.
The second is optional but if uploaded, I need to make sure its the correct type of file.
Other files can be uploaded as well to store and I just store then as is. (no verification).

I'm using the following to test the endpoint

Using httpx,

files = [
   ( "file_a", ("file_a.txt", open("file_a.txt", "rb"), "text/plain") ),
   ( "file_b", ("file_b.txt", open("file_b.txt", "rb"), "text/plain") )
   [
         ( "files_extra", ("file_c.txt", open("file_c.txt", "rb"), "text/plain") ),
         ( "files_extra", ("file_d.txt", open("file_d.txt", "rb"), "text/plain") ),
         ( "files_extra", ("file_e.txt", open("file_e.txt", "rb"), "text/plain") )
   ]
]
response = httpx.post(url, files=files)
response.raise_for_status()

But I get a 422 Error and this

{'detail': [{'type': 'list_type',
   'loc': ['body', 'other_files'],
   'msg': 'Input should be a valid list',
   'input': {'filename': 'file_c.txt',
    'file': {'_file': {},
     '_max_size': 1048576,
     '_rolled': False,
     '_TemporaryFileArgs': {'mode': 'w+b',
      'buffering': -1,
      'suffix': None,
      'prefix': None,
      'encoding': None,
      'newline': None,
      'dir': None,
      'errors': None}},
    'size': 1408,
    'headers': {'content-disposition': 'form-data; name="files_extra"; filename="file_c.txt"',
     'content-type': 'text/plain'}}}]}

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.112.0

Pydantic Version

2.8.2

Python Version

3.12.3

Additional Context

No response

[iamdhakrey]

@guzman109 you need to replace files_extra: Annotated[list[UploadFile] | None, File(description="Optional Extra Files")] = None to files_extra: Annotated[List[UploadFile], File(description="Optional Extra Files")] = [] because the combination of List[UploadFile] | None with File(...) creates a conflict. FastAPI expects a required file list due to File(...), but if it receives None (as might be the case when files are not provided), it leads to processing issues.

files = [
   ( "file_a", ("file_a.txt", open("file_a.txt", "rb"), "text/plain") ),
   ( "file_b", ("file_b.txt", open("file_b.txt", "rb"), "text/plain") )
-  [
+ # Each 'files_extra' is treated as a separate tuple, but they all share the same key
         ( "files_extra", ("file_c.txt", open("file_c.txt", "rb"), "text/plain") ),
         ( "files_extra", ("file_d.txt", open("file_d.txt", "rb"), "text/plain") ),
         ( "files_extra", ("file_e.txt", open("file_e.txt", "rb"), "text/plain") )
-  ]
]

[guzman109]

Thank you! All working now.