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Expense

This sample workflow processes an expense request. It demonstrates human-in-the loop processing and asynchronous activity completion.

Overview

This sample demonstrates the following workflow:

  1. Create Expense: The workflow executes the create_expense_activity to initialize a new expense report in the external system.

  2. Wait for Decision: The workflow calls wait_for_decision_activity, which demonstrates asynchronous activity completion. The activity registers itself for external completion using its task token, then calls activity.raise_complete_async() to signal that it will complete later without blocking the worker.

  3. Async Completion: When a human approves or rejects the expense, an external process uses the stored task token to call workflow_client.get_async_activity_handle(task_token).complete(), notifying Temporal that the waiting activity has finished and providing the decision result.

  4. Process Payment: Once the workflow receives the approval decision, it executes the payment_activity to complete the simulated expense processing.

This pattern enables human-in-the-loop workflows where activities can wait as long as necessary for external decisions without consuming worker resources or timing out.

Steps To Run Sample

  • You need a Temporal service running. See the main README.md for more details.
  • Start the sample expense system UI: 
    uv run -m expense.ui
  • Start workflow and activity workers: 
    uv run -m expense.worker
  • Start expense workflow execution: 
    uv run -m expense.starter
  • When you see the console print out that the expense is created, go to localhost:8099/list to approve the expense.
  • You should see the workflow complete after you approve the expense. You can also reject the expense.

Running Tests

# Run all tests
uv run pytest expense/test_workflow.py -v

# Run a specific test
uv run pytest expense/test_workflow.py::TestSampleExpenseWorkflow::test_workflow_with_mock_activities -v

Key Concepts Demonstrated

  • Human-in-the-Loop Workflows: Long-running workflows that wait for human interaction
  • Async Activity Completion: Using activity.raise_complete_async() to indicate an activity will complete asynchronously, then calling complete() on a handle to the async activity.
  • External System Integration: Communication between workflows and external systems via web services.

Troubleshooting

If you see the workflow failed, the cause may be a port conflict. You can try to change to a different port number in __init__.py. Then rerun everything.

Files

  • workflow.py - The main expense processing workflow
  • activities.py - Three activities: create expense, wait for decision, process payment
  • ui.py - A demonstration expense approval system web UI
  • worker.py - Worker to run workflows
  • starter.py - Client to start workflow executions by submitting an expense report