Caller pattern

The handler worker starts a GreetingWorkflow for a User ID. NexusGreetingServiceHandler derives the Workflow ID and routes every Nexus operation to it. The caller's input does not have that Workflow ID as the caller doesn't know it -- but the caller sends in the User ID, and NexusGreetingServiceHandler knows how to get the desired Workflow ID from that User ID (see the get_workflow_id call).

The handler worker uses the same get_workflow_id call to generate a Workflow ID from a User ID when it launches the Workflow.

The caller Workflow:

1. Queries for supported languages (get_languages -- backed by a @workflow.query)
2. Changes the language to Arabic (set_language -- backed by a @workflow.update that calls an activity)
3. Confirms the change via a second query (get_language)
4. Approves the Workflow (approve -- backed by a @workflow.signal)

Running

This sample requires a Temporal dev server build that supports Workflow Update callbacks. Download the compatible binary from the Temporal CLI pre-release instructions.

Start the Temporal dev server with the required namespaces pre-created and Workflow Update callbacks enabled:

./temporal server start-dev \
  --dynamic-config-value history.enableUpdateCallbacks=true \
  --dynamic-config-value history.enableCHASMSignalBacklinks=true \
  --namespace nexus-messaging-handler-namespace \
  --namespace nexus-messaging-caller-namespace

Create the Nexus endpoint:

./temporal operator nexus endpoint create \
  --name nexus-messaging-nexus-endpoint \
  --target-namespace nexus-messaging-handler-namespace \
  --target-task-queue nexus-messaging-handler-task-queue

In one terminal, start the handler worker:

uv run python -m nexus_messaging.callerpattern.handler.worker

In another terminal, run the following command to start the example:

uv run python -m nexus_messaging.callerpattern.caller.app

Expected output:

Supported languages: [<Language.CHINESE: 2>, <Language.ENGLISH: 3>]
Language changed: ENGLISH -> ARABIC
Workflow approved