Recommendations on waiting for a condition to happen

[jasonroelofs]

I have a workflow that needs to hold on a specific step until some other processes update database records. I initially implemented this as a RetryAfterError to tell inngest to keep retrying however, as it's an "error", it then fails the entire workflow after the default number of retries.

What I want is for this step to execute every so often and only continue onto the next step once the database condition is met (which I could make work by pushing the allowed number of retries really high but that feels like a hack). What is the recommended way for implementing such logic? Should I make the step itself loop and sleep? Is the expectation that the other part of the app will emit a new event and I use waitForEvent here? I'm having a hard time finding answers to this in the docs.

Thanks!

[tonyhb]

Hey @jasonroelofs - yes, this is exactly what step.waitForEvent is for. It'll pause your function, set up a new signal, and automatically resolve whenever the matching event is found.

If you then instrument other parts of your app with events (free our side, and a low implementation cost) you'll automatically resume those functions.

Typically, it'd be something like this:

await step.waitForEvent("some-step-id", {
  event: "api/something.happened", // format: <service>/<noun>
  timeout: "12h",
  if: `async.data.completion_id == "${someVar}"`,
});

You probably want to store some sort of ID for the matching expression. Without more details, it's hard to know what identifiers you can use to resolve these matches — but this is the general idea!

[jasonroelofs]

Sounds good, thanks for the confirmation!