How to update a state variable from a FastAPI POST route?

[erick-dumas]

Hi! I’m new to Reflex and I’m trying to connect it with FastAPI.
I created a POST route in FastAPI that receives some data, and I’d like to update a variable in a Reflex state (for example IndexState.last_temperature) when that POST is received.

What is the correct way to modify a state variable from a FastAPI route?
Is there any example or recommended approach for doing this?

Thanks in advance — I’m just getting started with Reflex and trying to learn!

[masenf]

first you need to send the token through with your POST request -- get can get this from sessionStorage.get("token") or by calling getToken from $/utils/state.js.

then you need to use that token to get the associated state and modify it

async with app.modify_state(f"{token}_{IndexState.get_full_name}") as root_state:
    index_state = await root_state.get_state(IndexState)
    index_state.last_temperature = value_from_request

when the context exits, the value will be persisted and sent to the client (if they are still connected).

prior to 0.8.17, if the client had reconnected to a different app instance, then the update would not have been sent.

[erick-dumas]

Thank you!
That works fine.