How to pass parameter from main lambda handler to event handlerroute

[MaartenUreel]

Assume a main lambda method, where we construct some variable:

@logger.inject_lambda_context()
@event_source(data_class=LambdaFunctionUrlEvent)
def lambda_handler(event: LambdaFunctionUrlEvent, context: LambdaContext) -> dict:
    # Parse & construct some parameters
    parameters = dict(parse_qsl(event.decoded_body))

    # Create a CallContext object
    call_context = CallContext(db, parameters)

    return app.resolve(event, context)

What is a good way to pass this call_context variable to a route handler, e.g.:

@app.post("/dial_call_status")
def dial_call_status():
    # How to access call_context here?

[heitorlessa]

Hey @MaartenUreel, we don't provide a dependency injection (DI) feature in Event Handler at the moment, so you'd have to handle call_context in the context of your route -- Using your example, it'd look like:

@app.post("/dial_call_status")
def dial_call_status():
    parameters = dict(parse_qsl(app.current_event.decoded_body))

    # Create a CallContext object
    call_context = CallContext(db, parameters)

If your need is more advanced, we'd love to discuss how a DI would look like in a RFC format for Event Handler. As DI has some cognitive load, I'd be looking at (1) UX of providing/depending on X, (2) whether any Callable suffice, (3) whether we should call it only once if a dependency is used multiple times (e.g., cache=True), and (4) whether we want to limit the depth of a graph (e.g., sub-sub-sub-dependencies).

Thanks a lot!

[MaartenUreel]

OK; I hadded it to context.__dict__["call_context"] and was able to retrieve it in the handler with app.lambda_context.__dict__["call_context"] then; it's a bit hacky but it will do for now.

[MaartenUreel]

I opened up an RFC anyway because I find I have too much boilerplate code now in every request.
I hope I did it according to standards ;-)

[heitorlessa]

Thanks a lot, marking this as the answer and will comment in the RFC today ;)