pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>

[js-d-coder]

Hi,
I am returning an object which I fetch from database using Beanie ODM and returning it in FastAPI API response and the error I get is this:

  File "/Users/user/Developer/project/backend/app/routes/task.py", line 26, in get_task
    return JSONResponse(content=jsonable_encoder(task))
                                ^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/user/Developer/project/.venv/lib/python3.11/site-packages/fastapi/encoders.py", line 223, in jsonable_encoder
    obj_dict = _model_dump(
               ^^^^^^^^^^^^
  File "/Users/user/Developer/project/.venv/lib/python3.11/site-packages/fastapi/_compat.py", line 182, in _model_dump
    return model.model_dump(mode=mode, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/user/Developer/project/.venv/lib/python3.11/site-packages/pydantic/main.py", line 390, in model_dump
    return self.__pydantic_serializer__.to_python(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>

The code is something like this:

@router.get("/{id}", dependencies=[Security(get_current_user)], response_model=tasks.TaskLog)
async def get_task(
    task_id: PydanticObjectId,
):
    task: tasks.TaskLog = await tasks.TaskLog.get(task_id)
    return task

How do I fix this error in FastAPI? Apparently, Pydantic does not know how to serialize Beanie's ObjectId.

Beanie version 1.30.0
Pydantic version 2.9.2
FastAPI version 0.115.13

[adeelsohailahmed]

Do you still get the same error with the latest Beanie version?

[js-d-coder]

My bad, I forgot to add version of the libraries. And, yes I am using latest Beanie version.