How can a field be updated rapidly once the onUpdate Firestore trigger has executed?

edit

To update a field rapidly once the onUpdate Firestore trigger has executed, you can use Cloud Functions with Cloud Firestore. You can create a Cloud Function that updates the field in real-time whenever the onUpdate trigger is triggered. Here's an example of how to do this:

1. Create a Cloud Function that triggers when an update occurs in Firestore.

2. In the Cloud Function, get the data that was updated.

3. Update the field that you want to change.

4. Save the updated data back to Firestore.

Here's an example of how to update the username field of a document in Firestore once the onUpdate trigger has executed:

exports.updateUsername = functions.firestore
  .document('users/{userId}')
  .onUpdate((change, context) => {
    const newValue = change.after.data();
    const previousValue = change.before.data();
    const uid = context.params.userId;

    // Check if username was updated
    if (newValue.username !== previousValue.username) {
      // Update the username field
      const updatedData = { username: newValue.username };

      // Save the updated data back to Firestore
      return admin.firestore()
        .collection('users')
        .doc(uid)
        .update(updatedData);
    } else {
      return null;
    }
  });

In this example, the Cloud Function is triggered when an update occurs in the users collection in Firestore. It then checks if the username field was updated and if so, it updates the username field with the new value. Finally, it saves the updated data back to Firestore.