Unsubscribing in GraphQL - Step-by-Step Execution

Concept Flow - Unsubscribing

Start Subscription

↓

Receive Data Stream

↓

Check Unsubscribe Request?

No→Continue Receiving

Yes↓

Stop Data Stream

↓

Clean Up Resources

↓

End

This flow shows how a GraphQL subscription starts, receives data, checks if the client wants to unsubscribe, and then stops and cleans up.

Execution Sample

GraphQL

subscription {
  newMessages {
    id
    content
  }
}

// Later client calls unsubscribe()

This subscription listens for new messages and later the client unsubscribes to stop receiving updates.

Execution Table

Step	Action	State	Result
1	Start subscription	Subscribed	Listening for newMessages
2	Receive new message	Subscribed	Data received: message with id and content
3	Client calls unsubscribe()	Unsubscribing	Stopping data stream
4	Clean up resources	Unsubscribed	No more data received
5	Attempt to receive data	Unsubscribed	No data received, subscription ended

💡 Client unsubscribed, so subscription stopped and no more data is received.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
subscriptionState	None	Subscribed	Subscribed	Unsubscribing	Unsubscribed	Unsubscribed
dataReceived	None	None	Message data	Message data	None	None

Key Moments - 2 Insights

Why does the subscription stop receiving data after unsubscribe is called?

Because at Step 3 in the execution_table, the client calls unsubscribe(), which changes the subscriptionState to 'Unsubscribing' and then 'Unsubscribed' at Step 4, stopping the data stream.

Can the client receive data after unsubscribing?

No, as shown in Step 5 of the execution_table, after unsubscribing, the subscriptionState is 'Unsubscribed' and no data is received.

Visual Quiz - 3 Questions

Look at the execution_table, what is the subscriptionState after Step 2?

A Unsubscribing

B Subscribed

C Unsubscribed

D None

💡 Hint

Check the 'State' column at Step 2 in the execution_table.

At which step does the client call unsubscribe()?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look for the action 'Client calls unsubscribe()' in the execution_table.

If the client never calls unsubscribe(), what would happen at Step 5?

A SubscriptionState would be 'Unsubscribing' and data would stop

B SubscriptionState would be 'Unsubscribed' and no data received

C SubscriptionState would be 'Subscribed' and data would continue to be received

D SubscriptionState would be 'None' and no data received

💡 Hint

Refer to the variable_tracker and execution_table showing subscriptionState changes.

Concept Snapshot

GraphQL subscriptions start by opening a data stream.
Client receives real-time data until it calls unsubscribe().
Unsubscribe stops the stream and cleans up resources.
After unsubscribing, no more data is received.
Always call unsubscribe to avoid resource leaks.

Full Transcript

This visual execution shows how a GraphQL subscription works and how unsubscribing stops the data stream. First, the subscription starts and listens for new messages. When a new message arrives, the client receives it. Later, the client calls unsubscribe(), which changes the subscription state to unsubscribing and then unsubscribed. This stops the data stream and cleans up resources. After unsubscribing, no more data is received. This process helps manage resources and avoid unnecessary data flow.

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