Subscription resolvers in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a subscription resolver in GraphQL?

A subscription resolver is a special function in GraphQL that listens for real-time events and sends updates to clients when data changes.

beginner

How does a subscription resolver differ from a query resolver?

A query resolver fetches data once when requested, while a subscription resolver keeps a connection open to send data updates continuously.

intermediate

What role does PubSub play in subscription resolvers?

PubSub is a system that helps subscription resolvers by publishing events and allowing clients to subscribe to those events for real-time updates.

intermediate

Why do subscription resolvers use WebSockets?

WebSockets keep a live connection between client and server, enabling subscription resolvers to push data instantly without repeated requests.

advanced

What is the typical structure of a subscription resolver function?

It usually has a subscribe method that returns an AsyncIterator to listen for events, and optionally a resolve method to process the event data before sending.

What does a subscription resolver primarily do?

A Listens for real-time data changes and sends updates

B Fetches data once on request

C Deletes data from the database

D Updates data in the database

Subscription resolvers listen for events and send real-time updates to clients.

Which protocol is commonly used to maintain live connections for subscriptions?

A WebSocket

B FTP

C HTTP

D SMTP

WebSocket keeps a persistent connection needed for real-time subscriptions.

In GraphQL subscriptions, what does PubSub help with?

A Query optimization

B Schema validation

C Publishing and subscribing to events

D Authentication

PubSub manages event publishing and subscription for real-time updates.

What does the subscribe method in a subscription resolver return?

A A Promise

B An AsyncIterator

C A Boolean

D A String

The subscribe method returns an AsyncIterator to listen for events.

Which of these is NOT a feature of subscription resolvers?

A Event listening

B Continuous data updates

C Real-time communication

D Single data fetch

Subscription resolvers do not fetch data just once; they provide continuous updates.

Explain how subscription resolvers work in GraphQL and why they are useful.

Think about how apps get live data like chat messages or notifications.

Describe the difference between query resolvers and subscription resolvers in GraphQL.

Compare a snapshot photo to a live video stream.