Creating workflows with multiple state transitions

Community Support
1

What are the patterns we can use for creating workflows with multiple state transitions?

I found one pattern in the nextjs-ecommerce-oneclick example where a local variable called purchaseState is used to maintain the state of the workflow and is transitioned to new states when signals are received. Also a wf.condition is used to terminate the workflow:

type PurchaseState = 'PURCHASE_PENDING' | 'PURCHASE_CONFIRMED' | 'PURCHASE_CANCELED';

export const cancelPurchase = wf.defineSignal('cancelPurchase');
export const purchaseStateQuery = wf.defineQuery<PurchaseState>('purchaseState');

export async function OneClickBuy(itemId: string) {
  const itemToBuy = itemId;
  let purchaseState: PurchaseState = 'PURCHASE_PENDING';
  wf.setHandler(cancelPurchase, () => void (purchaseState = 'PURCHASE_CANCELED'));
  wf.setHandler(purchaseStateQuery, () => purchaseState);
  if (await wf.condition(() => purchaseState === 'PURCHASE_CANCELED', '5s')) {
    return await canceledPurchase(itemToBuy);
  } else {
    purchaseState = 'PURCHASE_CONFIRMED';
    return await checkoutItem(itemToBuy);
  }
}

However, this is a simple workflow with only two states and one transition. How do I extend this pattern to multiple transitions? Taking an uber workflow example (and this is just the happy path),

 received ride request
 -> send ride options
 -> received selected option
 -> send ride details
 -> start ride
 -> end ride
 -> send receipt

My initial thought was to use if... else if... else if..., but that seems quite cumbersome. Something like a switch would have been nice, but I feel like I am missing something. What are the common patterns for this scenario? Any examples?

2

Thinking more, to chain more transitions, one should not return from the workflow until it is fully done. So in the e-commerce example above, extending it to one more transition could be done like this:

type PurchaseState = 'PURCHASE_PENDING' | 'PURCHASE_CONFIRMED' | 'CHECKOUT_COMPLETED' | 'PURCHASE_CANCELED';

export const cancelPurchase = wf.defineSignal('cancelPurchase');
export const checkout = wf.defineSignal('checkout');
export const purchaseStateQuery = wf.defineQuery<PurchaseState>('purchaseState');

export async function OneClickBuy(itemId: string) {
  const itemToBuy = itemId;
  let purchaseState: PurchaseState = 'PURCHASE_PENDING';
  wf.setHandler(cancelPurchase, () => void (purchaseState = 'PURCHASE_CANCELED'));
  wf.setHandler(checkout, () => void (purchaseState = 'CHECKOUT_COMPLETED'));
  wf.setHandler(purchaseStateQuery, () => purchaseState);

  if (await wf.condition(() => purchaseState === 'PURCHASE_CANCELED', '5s')) {
    return await canceledPurchase(itemToBuy);
  } else {
    purchaseState = 'PURCHASE_CONFIRMED';
    // ----- DON'T RETURN HERE -----
    await checkoutItem(itemToBuy);
  }

  if (await wf.condition(() => purchaseState === 'CHECKOUT_COMPLETED', '5s')) {
    return await sendInvoice(itemToBuy);
  } else {
    purchaseState = 'PURCHASE_CANCELED';
    return await canceledPurchase(itemToBuy);
  }
}

Does this work? Any other better approach?

3

Updating the state variables from signals and using the condition to block workflow progress according to its state works well in many cases.

1 Like
4

Thank you for confirming @maxim.