FastAPI – How to get app instance inside a router?

Question

I want to get the app instance in my router file, what should I do ?

My main.py is as follows:

# ...
app = FastAPI()
app.machine_learning_model = joblib.load(some_path)
app.include_router(some_router)
# ...

Now I want to use app.machine_learning_model in some_router’s file , what should I do ?

Asked By: DachuanZhao

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Source

Answer 1

Since FastAPI is actually Starlette underneath, you could store the model on the app instance using the generic app.state attribute, as described in Starlette’s documentation (see State class implementation too). Example:

app.state.ml_model = joblib.load(some_path)

As for accessing the app instance (and subsequently, the model) from outside the main file, you can use the Request object. As per Starlette’s documentation, where a request is available (i.e., endpoints and middleware), the app is available on request.app. Example:

from fastapi import Request

@router.get('/')
def some_router_function(request: Request):
    model = request.app.state.ml_model

Answered By: Chris

FastAPI – How to get app instance inside a router?

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