ensure-lookup-can-be-retried.md

Ensure Lookup Can Be Retried

A common thing to do in a workflow step is to look up a record. This might be a record that was created or updated around the time that the workflow was triggered.

You need to be sure the record was found before proceeding. That might end up looking like this:

export default inngest.createFunction(
  { id: "record-user-purchase" },
  { event: "app/record.purchase" },
  async ({ event, step }) => {
    const checkoutSession =
      await step.run("find checkout session", async () => {
        const cs = provider.lookupSession(event.checkoutSessionId)

        return cs;
      });

    if(!checkoutSession) {
      throw new Error('Checkout session not found')
    }
  }
);

This approach has a subtle problem which is that the error for a missing checkout session is raised outside the step that sets checkoutSession. As inngest does a series of retries, the memorized checkoutSession step won't be rerun and the error will continue to be thrown.

It is better to raise the error within the lookup step:

export default inngest.createFunction(
  { id: "record-user-purchase" },
  { event: "app/record.purchase" },
  async ({ event, step }) => {
    const checkoutSession =
      await step.run("find checkout session", async () => {
        const cs = provider.lookupSession(event.checkoutSessionId)

        if(!cs) {
          throw new Error('Checkout session not found')
        }

        return cs;
      });
  }
);

If the checkout session is missing on the first couple tries, the step will have a chance to retry the lookup and maybe eventually find what it is looking for.