Injecting key, values into APIGatewayRestResolver object

[SeanCoaker]

Hi,

We're currently using around 10 lambda functions as proxy integrations with APIGateway endpoints. When running our lambda_handler functions, we wish to inject a user class collected from Cognito into the event that is passed into APIGatewayRestResolver.resolve.

We have a couple ideas for doing this in an abstracted and repeatable manner. Firstly, build a decorator which injects user attributes as key, value pairs into the lambda event dict, before running APIGatewayRestResolver.resolve on that event. Secondly, build an extended class from the APIGatewayRestResolver class and add the user class injection as part of the resolve function.

We were wondering if APIGatewayRestResolver already has an automated way for injecting extra data ito the event as part of the resolve function call, or if anyone had any better suggestions for solving this problem?

Thank you

[leandrodamascena]

Hi @SeanCoaker, this is a very interesting question that customers always ask about dependency injection for various reasons: testing, code reuse, and others. Personally, I use dependency injection whenever I can, it makes a lot of things easier.

While our app.resolve(event, context) function doesn't support dependency injection directly on this, which makes sense because we focus on solving problems to resolve AWS events coming into Lambda, we do allow you to share data/classes/others through what we call contextual data. You can inject data before invoke app.resolve() and all routes will have access to that.

I created an example that can help you.

from aws_lambda_powertools import Logger
from aws_lambda_powertools.event_handler import APIGatewayRestResolver
from aws_lambda_powertools.logging import correlation_paths
from aws_lambda_powertools.utilities.typing import LambdaContext

logger = Logger()
app = APIGatewayRestResolver()

class MyInjectedDependency:

    def __init__(self, name: str) -> None:
        self.name = name

    def return_name(self):
        return self.name

@app.get("/hello")
def get_hello():

    my_injected_dependency: MyInjectedDependency = app.context.get("my_injected_dependency")
    return {"my_dependency_type": str(type(my_injected_dependency)), "my_dependency_method": my_injected_dependency.return_name()}


# You can continue to use other utilities just as before
@logger.inject_lambda_context(correlation_id_path=correlation_paths.API_GATEWAY_REST)
def lambda_handler(event: dict, context: LambdaContext) -> dict:
    app.append_context(my_injected_dependency=MyInjectedDependency(name="powertools"))
    return app.resolve(event, context)

Please let me know if it help you to solve your question. Have a good day.

[SeanCoaker]

Hi @leandrodamascena. Thank you for your timely and detailed response. It is very helpful and certainly gives us further options to consider going forward. :)

[leandrodamascena]

I'm glad to hear that, @SeanCoaker! Please let me know if you have any additional questions!

If you see room for any improvement, feel free to open an issue and submit a PullRequest, we love having community contributors to Powertools. 🚀

[leandrodamascena]

Also, I don't know if you read about this, but we support Middlewares in this event handler resolver and you may find it useful in some situations.

https://docs.powertools.aws.dev/lambda/python/latest/core/event_handler/api_gateway/#middleware