Child workflows | pg-workflows

step.invokeChildWorkflow starts another workflow, pauses the parent, and returns the child's output when the child completes. The parent holds no worker while it waits.

import { createWorkflowRef, workflow } from 'pg-workflows'
import { z } from 'zod'

type ReceiptOutput = { receiptId: string }
const receiptInput = z.object({ orderId: z.string() })

// Explicit generics turn off inference, so pass the schema type as the second one
const sendReceiptRef = createWorkflowRef<ReceiptOutput, typeof receiptInput>('send-receipt', {
  inputSchema: receiptInput,
})

export const sendReceipt = sendReceiptRef(async ({ step, input }) => {
  return step.run('email-receipt', async () => ({ receiptId: `rcpt_${input.orderId}` }))
})

export const checkout = workflow(
  'checkout',
  async ({ step, input }) => {
    const receipt = await step.invokeChildWorkflow('send-receipt', sendReceiptRef, {
      orderId: input.orderId,
    })
    return { receiptId: receipt.receiptId } // receipt: ReceiptOutput
  },
  { inputSchema: z.object({ orderId: z.string() }) },
)

Register both checkout and sendReceipt with the engine. You can also invoke by ID and type the output with a generic:

const receipt = await step.invokeChildWorkflow<ReceiptOutput>('send-receipt', {
  workflowId: 'send-receipt',
  input: { orderId: input.orderId },
})

Behavior:

The child starts once per parent step. Its output is saved on the parent like any step result.
If the child fails or is cancelled, the parent step throws, and the parent's own retries apply.
The child inherits the parent's priority unless the call or the child's definition sets one.
Cancelling the parent does not cancel the child. The child runs to its own end state. The same applies when the parent fails, completes, or times out while the child is running.
resumeWorkflow() and fastForwardWorkflow() do nothing while the parent waits on a child.