Why subscriptions enable real-time data in GraphQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a subscription that listens for new messages.

GraphQL

subscription { [1] newMessage { id content } }

Drag options to blanks, or click blank then click option'

Aon

Badded

Clisten

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'added' instead of 'on' causes syntax errors.

Using 'subscribe' or 'listen' are not valid GraphQL keywords here.

The keyword on is used to specify the event to listen to in a subscription.

2fill in blank

medium

Complete the subscription to receive real-time updates for user status changes.

GraphQL

subscription { [1] userStatusChanged { userId status } }

Drag options to blanks, or click blank then click option'

Alisten

Bwatch

Ctrigger

Don

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'trigger' or 'watch' are not valid GraphQL subscription syntax.

Forgetting the keyword causes syntax errors.

The on keyword is used to specify the event in a subscription.

3fill in blank

hard

Fix the error in the subscription to correctly listen for new comments.

GraphQL

subscription { [1] newComments { id text author } }

Drag options to blanks, or click blank then click option'

Alisten

Bwatch

Con

Dsubscribe

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'subscribe' instead of 'on' causes syntax errors.

Using 'listen' or 'watch' are not valid GraphQL keywords here.

The correct keyword to specify the event in a subscription is on.

4fill in blank

hard

Fill both blanks to complete the subscription that listens for order updates with id and status fields.

GraphQL

[1] { [2] orderUpdated { id status } }

Drag options to blanks, or click blank then click option'

Aon

Bsubscription

Cquery

Dmutation

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'query' or 'mutation' instead of 'subscription' for the operation.

Using 'query' or 'mutation' inside the subscription block.

The subscription operation starts with the keyword subscription, and inside it, the event is specified with on.

5fill in blank

hard

Fill both blanks to complete the subscription that listens for chat messages with id, text, and sender fields.

GraphQL

[1] { [2] chatMessageReceived { id text sender } }

Drag options to blanks, or click blank then click option'

Asubscription

Bon

Cquery

Dmutation

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'query' or 'mutation' instead of 'subscription' for the operation.

Omitting the 'on' keyword inside the subscription.

The subscription operation starts with subscription, the event uses on.

Practice

1. What is the main reason GraphQL subscriptions enable real-time data updates?

easy

A. They only work with static data queries.

B. They require the client to repeatedly ask for data.

C. They store data locally on the client device.

D. They keep a connection open to push new data instantly.

Solution

1. Step 1: Understand how subscriptions work

   Subscriptions maintain an open connection between client and server.

2. Step 2: Identify the benefit of this connection

   This open connection allows the server to send data updates immediately when they happen.

3. Final Answer:

   They keep a connection open to push new data instantly. -> Option D

4. Quick Check:

   Open connection = real-time updates [OK]

Hint: Subscriptions push data without repeated requests [OK]

Common Mistakes:

• Thinking subscriptions require repeated client requests
• Confusing subscriptions with local data storage
• Believing subscriptions only work with static data

2. Which of the following is the correct syntax to define a GraphQL subscription named newMessage?

easy

A. mutation { newMessage { id content } }

B. query { newMessage { id content } }

C. subscription { newMessage { id content } }

D. subscription newMessage { id content }

Solution

1. Step 1: Identify the correct operation type

   Subscriptions use the keyword subscription to define real-time data streams.

2. Step 2: Check the syntax structure

   The correct syntax wraps the subscription name inside braces with requested fields: subscription { newMessage { id content } }.

3. Final Answer:

   subscription { newMessage { id content } } -> Option C

4. Quick Check:

   Subscription keyword + braces = correct syntax [OK]

Hint: Subscriptions start with 'subscription' keyword [OK]

Common Mistakes:

• Using 'query' or 'mutation' instead of 'subscription'
• Missing braces around subscription fields
• Incorrect placement of subscription name

3. Given this subscription query:

subscription { newNotification { id message } }

What will the client receive when a new notification is created?

medium

A. Continuous updates with each new notification's id and message.

B. Only the notification count, not details.

C. An error because subscriptions can't fetch notifications.

D. A one-time response with all past notifications.

Solution

1. Step 1: Understand the subscription query

   The query listens for new notifications and requests id and message fields.

2. Step 2: Determine the data flow

   Each time a new notification is created, the server pushes the new data to the client continuously.

3. Final Answer:

   Continuous updates with each new notification's id and message. -> Option A

4. Quick Check:

   Subscription pushes new data continuously [OK]

Hint: Subscriptions send updates continuously, not once [OK]

Common Mistakes:

• Thinking subscriptions send only past data once
• Assuming subscriptions cause errors for notifications
• Believing subscriptions send only counts, not details

4. Identify the error in this subscription definition:

subscription newMessage { id content }

medium

A. Using 'subscription' instead of 'query'.

B. Missing braces around the subscription fields.

C. Subscription name cannot be 'newMessage'.

D. Fields 'id' and 'content' are invalid in subscriptions.

Solution

1. Step 1: Check subscription syntax

   Subscriptions require braces around the fields to specify what data to return.

2. Step 2: Identify missing braces

   The given code lacks braces around id and content, causing a syntax error.

3. Final Answer:

   Missing braces around the subscription fields. -> Option B

4. Quick Check:

   Fields must be inside braces [OK]

Hint: Always wrap fields in braces in subscriptions [OK]

Common Mistakes:

• Confusing subscription with query syntax
• Thinking subscription names are restricted
• Assuming fields are invalid in subscriptions

5. You want to build a live chat app using GraphQL subscriptions. Which approach best ensures users see new messages instantly?

hard

A. Use a subscription that listens for new messages and pushes them to clients immediately.

B. Use a query that clients call every 5 seconds to fetch new messages.

C. Use a mutation to send messages but no subscription for updates.

D. Store messages locally and refresh the app manually.

Solution

1. Step 1: Understand real-time needs in chat apps

   Chat apps require instant updates when new messages arrive.

2. Step 2: Choose the best GraphQL feature

   Subscriptions keep a live connection to push new messages immediately to clients.

3. Step 3: Compare alternatives

   Polling queries cause delays; mutations alone don't push updates; manual refresh is slow.

4. Final Answer:

   Use a subscription that listens for new messages and pushes them to clients immediately. -> Option A

5. Quick Check:

   Subscriptions = instant push updates [OK]

Hint: Subscriptions push chat messages instantly [OK]

Common Mistakes:

• Using polling queries causing delay
• Relying only on mutations without subscriptions
• Expecting manual refresh for real-time updates