Async dependencies? #9460
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Hi there, I have found synchronous dependencies very easy to deal with @lru_cache()
def get_client() -> Client:
return Client( ... )
@app.get('/')
async def my_endpoint(client: Annotated[Client, Depends(get_client)]) -> dict[str, any] :
data = await client.fetch()
return dataBut I have found asynchronous much more convoluted to deal with This flat out doesn't work @lru_cache()
async def get_connection() -> Connection:
client = await AsyncClient.connection( ... )
return client
@app.get('/')
async def my_endpoint(client: Annotated[Connection, Depends(get_connection)]) -> dict[str, any] :
data = await client.fetch() # AttributeError: 'coroutine' object has no attribute 'fetch'
return dataYou have to resort to an untyped storage on app state async def get_connection() -> Connection:
client = await AsyncClient.connection( ... )
return client
@app.startup()
async def setup_connection() -> Connection:
app.state.connection = await get_connection()
@app.get('/')
async def my_endpoint(request: Request) -> dict[str, any] :
connection: Connection = request.app.state.connection
data = await client.fetch()
return dataIs there a well accepted general solution / standard procedure for dealing with async deps? |
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Replies: 2 comments 1 reply
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Here is how I did it 6 months ago (I am not sure if things have changed since then) |
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If you don't like approach with @lru_cache()
def _get_client() -> Client:
return Client( ... )
async def get_client_async() -> Client:
return _get_client()
@app.get('/')
async def my_endpoint(client: Annotated[Client, Depends(get_client_async)]) -> dict[str, any] :
data = await client.fetch()
return data |
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Example with from typing import Annotated
from async_lru import alru_cache
from fastapi import Depends, FastAPI
app = FastAPI()
class Client:
pass
@alru_cache
async def get_client_async() -> Client:
print("Creating client...")
return Client()
@app.get("/")
async def my_endpoint(
client: Annotated[Client, Depends(get_client_async)],
):
return {"client": str(client)} |
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If you don't like approach with
lifespanandrequest.state, you can wrap your cached dependency function withasyncfunction: