Real-time updates with listeners in GCP - Mini Project: Build & Apply

Real-time updates with listeners

📖 Scenario: You are building a simple cloud application that needs to react instantly when data changes in a Firestore database. This is common in chat apps, live dashboards, or collaborative tools.

🎯 Goal: Create a Firestore listener that watches a collection called messages and prints new messages as they arrive.

📋 What You'll Learn

Create a Firestore client connection

Set up a listener on the messages collection

Handle real-time updates by printing new message data

Cleanly stop the listener when done

💡 Why This Matters

🌍 Real World

Real-time listeners are used in chat apps, live dashboards, and collaborative tools to update the UI instantly when data changes.

💼 Career

Understanding real-time updates with Firestore listeners is essential for cloud developers building responsive and interactive applications.

1

Set up Firestore client connection

Write code to create a Firestore client called db using the firestore.Client() constructor.

GCP

# Your code here to create Firestore client

Need a hint?

Use firestore.Client() to connect to Firestore.

2

Create a query for the messages collection

Create a variable called messages_ref that references the messages collection from db using db.collection('messages').

GCP

from google.cloud import firestore

db = firestore.Client()

# Create a reference to the 'messages' collection
# Your code here

Need a hint?

Use db.collection('messages') to get the collection reference.

3

Add a listener to handle real-time updates

Define a function called on_snapshot that takes docs, changes, read_time as parameters. Inside it, write a for loop over changes and print the document data for each change where change.type.name == 'ADDED'. Then, attach this listener to messages_ref using on_snapshot(on_snapshot) and save the returned callback to listener.

GCP

from google.cloud import firestore

db = firestore.Client()

messages_ref = db.collection('messages')

# Define on_snapshot function and attach listener
# Your code here

Need a hint?

Use on_snapshot to listen for changes and check for ADDED type.

4

Stop the listener cleanly

Call the unsubscribe() method on the listener variable to stop listening for updates.

GCP

from google.cloud import firestore

db = firestore.Client()

messages_ref = db.collection('messages')

def on_snapshot(docs, changes, read_time):
    for change in changes:
        if change.type.name == 'ADDED':
            print(f"New message: {change.document.to_dict()}")

listener = messages_ref.on_snapshot(on_snapshot)

# Stop the listener
# Your code here

Need a hint?

Call listener.unsubscribe() to stop the listener.