Unsubscribing in GraphQL - Mini Project: Build & Apply

GraphQL Subscription Unsubscribing

📖 Scenario: You are building a real-time chat application using GraphQL subscriptions. Users can subscribe to new messages in a chat room. To avoid receiving unwanted messages, users need to unsubscribe from the subscription when they leave the chat room.

🎯 Goal: Build a GraphQL subscription setup that allows subscribing to new messages and then unsubscribing properly to stop receiving updates.

📋 What You'll Learn

Create a GraphQL subscription called messageAdded that listens for new messages.

Create a variable called subscription to hold the subscription object.

Use the subscribe method to start the subscription and assign it to subscription.

Call the unsubscribe method on subscription to stop receiving messages.

💡 Why This Matters

🌍 Real World

Real-time applications like chat apps, live sports scores, or stock price updates use GraphQL subscriptions to get live data.

💼 Career

Understanding how to subscribe and unsubscribe in GraphQL is essential for building efficient and user-friendly real-time web applications.

1

Define the GraphQL subscription for new messages

Write a GraphQL subscription called messageAdded that listens for new messages with fields id and content.

GraphQL

subscription messageAdded {
  # Your code here
}

Hint

Use the subscription keyword and specify the fields id and content inside messageAdded.

2

Create a variable to hold the subscription object

Create a variable called subscription to hold the subscription object returned by the subscribe method.

GraphQL

subscription messageAdded {
  messageAdded {
    id
    content
  }
}

// Create a variable called subscription to hold the subscription object
// Your code here

Hint

Use const subscription = client.subscribe({ query: MESSAGE_ADDED }); to start the subscription.

3

Subscribe to the messageAdded subscription

Use the subscribe method on client with the MESSAGE_ADDED query and assign the result to the variable subscription.

GraphQL

subscription messageAdded {
  messageAdded {
    id
    content
  }
}

const subscription = client.subscribe({ query: MESSAGE_ADDED });

// Your code here to handle subscription data

Hint

Call subscription.subscribe with next and error handlers to receive messages.

4

Unsubscribe from the subscription

Call the unsubscribe method on the subscription object to stop receiving new messages.

GraphQL

subscription messageAdded {
  messageAdded {
    id
    content
  }
}

const subscription = client.subscribe({ query: MESSAGE_ADDED });

subscription.subscribe({
  next(data) {
    console.log('New message:', data);
  },
  error(err) {
    console.error('Subscription error:', err);
  }
});

// Call unsubscribe on subscription to stop updates
// Your code here

Hint

Simply call subscription.unsubscribe() to stop receiving messages.

Practice

1.

What does calling unsubscribe() on a GraphQL subscription do?

easy

A. It pauses the subscription but keeps the connection alive.

B. It restarts the subscription to receive updates again.

C. It deletes the subscription from the server permanently.

D. It stops receiving live updates from the subscription.

Solution

1. Step 1: Understand the purpose of unsubscribe()

   The unsubscribe() method is designed to stop live updates from a GraphQL subscription.

2. Step 2: Differentiate from other actions

   It does not restart, delete permanently, or pause the subscription; it simply stops updates.

3. Final Answer:

   It stops receiving live updates from the subscription. -> Option D

4. Quick Check:

   Unsubscribe() stops updates = D [OK]

Hint: Remember: unsubscribe() means stop updates completely [OK]

Common Mistakes:

• Thinking unsubscribe() restarts the subscription
• Confusing unsubscribe() with deleting the subscription
• Assuming unsubscribe() only pauses updates

2.

Which of the following is the correct syntax to stop a GraphQL subscription stored in variable sub?

const sub = client.subscribe({ query: MY_SUBSCRIPTION });
// Stop subscription here

easy

A. sub.stop();

B. unsubscribe(sub);

C. sub.unsubscribe();

D. client.unsubscribe(sub);

Solution

1. Step 1: Identify the unsubscribe method on subscription object

   The subscription object returned by client.subscribe() has an unsubscribe() method to stop it.

2. Step 2: Match correct syntax

   Calling sub.unsubscribe(); correctly stops the subscription. Other options are invalid method calls.

3. Final Answer:

   sub.unsubscribe(); -> Option C

4. Quick Check:

   Call unsubscribe() on subscription object = A [OK]

Hint: Use unsubscribe() method on the subscription variable [OK]

Common Mistakes:

• Using unsubscribe() as a standalone function
• Calling stop() instead of unsubscribe()
• Trying to unsubscribe via client object

3.

Given the code below, what will be logged after sub.unsubscribe() is called?

const sub = client.subscribe({ query: MY_SUBSCRIPTION });
sub.subscribe({
  next(data) { console.log('Received:', data); },
  error(err) { console.error('Error:', err); }
});

sub.unsubscribe();

// Later, server sends new data

medium

A. An error will be logged because subscription is closed.

B. No logs will appear after unsubscribe is called.

C. Logs will continue showing 'Received:' with new data.

D. Logs will show 'Received:' once more then stop.

Solution

1. Step 1: Understand unsubscribe effect on subscription callbacks

   Calling unsubscribe() stops the subscription and prevents further next callbacks.

2. Step 2: Predict logging behavior after unsubscribe

   Since subscription is stopped, no new data triggers console.log, so no logs appear after unsubscribe.

3. Final Answer:

   No logs will appear after unsubscribe is called. -> Option B

4. Quick Check:

   Unsubscribe stops callbacks = C [OK]

Hint: After unsubscribe, no more data callbacks occur [OK]

Common Mistakes:

• Expecting data logs after unsubscribe
• Assuming unsubscribe triggers an error
• Thinking one last data event logs after unsubscribe

4.

Identify the error in the code below that prevents unsubscribing correctly:

const subscription = client.subscribe({ query: NEW_MESSAGES });
subscription.next({
  next(data) { console.log(data); }
});

subscription.unsubscribe();

medium

A. Using subscription.next() instead of subscription.subscribe().

B. Calling unsubscribe() before subscribing.

C. Missing error callback in subscription.

D. Not assigning subscription to a variable.

Solution

1. Step 1: Check subscription method usage

   The subscription object uses subscribe() to listen for data, not next().

2. Step 2: Identify correct method to receive data

   Replacing subscription.next() with subscription.subscribe() fixes the issue and allows unsubscribe to work properly.

3. Final Answer:

   Using subscription.next() instead of subscription.subscribe(). -> Option A

4. Quick Check:

   Use subscribe(), not next(), to listen = B [OK]

Hint: Use subscribe() method to listen, not next() [OK]

Common Mistakes:

• Calling next() instead of subscribe()
• Unsubscribing before subscribing
• Ignoring error callback (not critical here)

5.

You have multiple active subscriptions stored in an array subs. How do you efficiently unsubscribe from all of them?

const subs = [sub1, sub2, sub3];
// Your code here

hard

A. subs.forEach(s => s.unsubscribe());

B. subs.unsubscribe();

C. for (let i = 0; i < subs.length; i++) { unsubscribe(subs[i]); }

D. subs.map(s => s.stop());

Solution

1. Step 1: Understand unsubscribing multiple subscriptions

   Each subscription object has an unsubscribe() method to stop it individually.

2. Step 2: Use array iteration to call unsubscribe on each

   Using subs.forEach(s => s.unsubscribe()); calls unsubscribe on all subscriptions efficiently.

3. Final Answer:

   subs.forEach(s => s.unsubscribe()); -> Option A

4. Quick Check:

   Call unsubscribe() on each subscription in array = A [OK]

Hint: Use forEach to unsubscribe all in array [OK]

Common Mistakes:

• Calling unsubscribe() on the array itself
• Using stop() method which does not exist
• Trying to call unsubscribe() without iteration