Undefined Firestore Document Data in Firebase Functions Gen 2 Trigger

When using Firebase Functions Gen 2, the trigger function now follows the CloudEvents format. In other words, the function’s callback signature has changed compared to Gen 1. Instead of receiving an object with a legacy event.data and event.params, the event is now a CloudEvent whose Firestore data is nested (for example, in data.value), and the parameters aren’t automatically pulled out.

To resolve your issue, you can update your code to use the new callback signature that separates the snapshot (or “data”) and context (which provides your parameters). For an onDocumentCreated trigger, you might change your function from:

JAVASCRIPTCopied
// Old-style single parameter (Gen 1 signature)
exports.staging_chat_notif = functions.firestore.onDocumentCreated(
  'messages/{id}',
  async (event) => {
    console.log('Raw Event Data:', event);
    const stagingVariables = getNotificationVariables('staging');
    return handleChatNotification(event, stagingVariables);
  }
);

to a Gen 2 style callback that receives the document snapshot and context separately:

JAVASCRIPTCopied
exports.staging_chat_notif = functions.firestore.document('messages/{id}')
  .onCreate(async (snapshot, context) => {
    // Log the document snapshot data
    const docData = snapshot.data();
    console.log('Document Data:', docData);
    console.log('Document ID:', context.params.id);
    
    const stagingVariables = getNotificationVariables('staging');
    return handleChatNotification({ data: docData, id: context.params.id }, stagingVariables);
  });

Key Points:

1. Event Format:
   In Gen 2, your trigger function is using the CloudEvents format. If you try to access event.data or event.params directly (as in Gen 1), those will be undefined. You’ll need to use the new callback parameters (e.g., snapshot for the new document data and context for parameters such as id).

2. Deployment Configuration:
   Your deployment command looks correct for a Gen 2 Firestore onDocumentCreated trigger. The --trigger-event-filters-path-pattern="document=messages/{id}" setting defines the path, so ensure that your function code uses that parameter in its signature.

3. Recommended Approach:
   Use the dedicated .document(...).onCreate((snapshot, context) => { ... }) method when working with Cloud Firestore triggers in Gen 2. This pattern simplifies access to the document snapshot (with snapshot.data()) and route parameters (via context.params).

With these changes, your function should correctly log the document’s content and ID, and your event data (payload) will be accessible as expected.