Partial update in FastAPI

I want to implement a put or patch request in FastAPI that supports partial update. The official documentation is really confusing and I can’t figure out how to do the request. (I don’t know that items is in the documentation since my data will be passed with request’s body, not a hard-coded dict).

class QuestionSchema(BaseModel):
    title: str = Field(..., min_length=3, max_length=50)
    answer_true: str = Field(..., min_length=3, max_length=50)
    answer_false: List[str] = Field(..., min_length=3, max_length=50)
    category_id: int


class QuestionDB(QuestionSchema):
    id: int


async def put(id: int, payload: QuestionSchema):
    query = (
        questions
        .update()
        .where(id == questions.c.id)
        .values(**payload)
        .returning(questions.c.id)
    )
    return await database.execute(query=query)

@router.put("/{id}/", response_model=QuestionDB)
async def update_question(payload: QuestionSchema, id: int = Path(..., gt=0),):
    question = await crud.get(id)
    if not question:
        raise HTTPException(status_code=404, detail="question not found")

    ## what should be the stored_item_data, as documentation?
    stored_item_model = QuestionSchema(**stored_item_data)
    update_data = payload.dict(exclude_unset=True)
    updated_item = stored_item_model.copy(update=update_data)

    response_object = {
        "id": question_id,
        "title": payload.title,
        "answer_true": payload.answer_true,
        "answer_false": payload.answer_false,
        "category_id": payload.category_id,
    }
    return response_object

How can I complete my code to get a successful partial update here?

Answer

I got this answer on the FastAPI’s Github issues.

You could make the fields Optional on the base class and create a new QuestionCreate model that extends the QuestionSchema. As an example:

from typing import Optional

class Question(BaseModel):
    title: Optional[str] = None  # title is optional on the base schema
    ...

class QuestionCreate(Question):
   title: str  # Now title is required

The cookiecutter template here provides some good insight too.