Graph Compose

Polling Conditions 🔄

Master the art of handling long-running tasks! Learn how to make your workflow wait for operations to complete.

🚀 When do I need this? Use polling when your workflow needs to wait for an operation to complete or a state to be reached:

  • 🔄 Long-running Jobs: Wait for tasks like data processing or report generation to finish.
  • ⏳ Resource Provisioning: Ensure resources like databases or servers are ready before proceeding.
  • 📊 Progress Tracking: Monitor the status of operations like file uploads or asynchronous API calls.
  • 🌐 External API Operations: Wait for external services (e.g., payment processing) to confirm completion.
  • 🛡️ Building Reliable Systems: Handle scenarios where you need to confirm a state before moving on.
View Complete Polling Conditions Schema

Common Polling Examples

Here are some typical polling conditions you might use:

// Wait for a job to complete
conditions: {
  pollUntil: ["{{ status = 'completed' }}"]
}

Real World Example 🌟

Here's a common scenario where polling is essential - processing a large dataset:

import { GraphCompose } from '@graph-compose/client';

const workflow = new GraphCompose()
  // 🚀 Step 1: Start the data processing job
  .node('start_job')
    .post('http://api.example.com/jobs')
    .withBody({
      type: 'process_data'
    })
  .end()

  // 🔄 Step 2: Poll the job status until it's complete
  .node('check_status')
    .withDependencies(['start_job'])
    .get('http://api.example.com/jobs/{{results.start_job.jobId}}')
    // ⏱️ Step 3: The retry policy controls how often we check
    .withRetries({
       initialInterval: '1 second',
       maximumAttempts: 3,
       maximumInterval: '1 second'
    })
    .withConditions({
      pollUntil: ["{{ status = 'completed' }}"] // Wait until status is 'completed'
    })
  .end();
  // 💡 Step 4: Workflow continues automatically after 'check_status' completes

How It Works 🔧

Polling is simple but powerful:

  1. Make an HTTP request
  2. Check if pollUntil condition is true
  3. If true → continue workflow
  4. If false → retry based on retry policy
  5. Repeat until success or max attempts reached

⚠️ Important:

  • The pollUntil condition must evaluate to a boolean value
  • Use activityConfig.retryPolicy to control polling frequency and limits
  • The condition is evaluated against the response data
  • Variables from previous nodes can be accessed via results

Advanced Usage 🚀

Combining with Flow Control

You can combine polling with Flow Control for complex scenarios:

{
  "id": "check_status",
  "type": "http",
  "conditions": {
    "pollUntil": ["{{ status != 'in_progress' }}"],
    "terminateWhen": ["{{ status = 'failed' }}"],
    "continueTo": [
      {
        "to": "process_results",
        "when": "{{ status = 'completed' }}"
      }
    ]
  }
}

This setup:

  1. 🔄 Polls until status changes from 'in_progress'
  2. 🛑 Terminates if status is 'failed'
  3. ✨ Continues to process results if completed