Subscription filtering in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is subscription filtering in GraphQL?

Subscription filtering means sending only specific updates to clients based on conditions they care about. It helps avoid sending unnecessary data.

beginner

Why use subscription filtering?

It saves bandwidth and improves performance by sending only relevant data to each client instead of all updates.

intermediate

How do you apply filters in a GraphQL subscription?

You add arguments to the subscription field that specify conditions. The server checks these conditions and sends updates only if they match.

intermediate

Example: Filtering a chat message subscription by room ID

subscription OnMessage($roomId: ID!) { messageAdded(roomId: $roomId) { id content } } This sends messages only from the specified room.

beginner

What happens if no filter is applied in a subscription?

The client receives all updates for that subscription, which can cause unnecessary data transfer and slower performance.

What is the main benefit of subscription filtering?

A All data is sent to every client

B Only relevant updates are sent to clients

C Subscriptions run faster on the client

D It removes the need for queries

Subscription filtering ensures clients get only the updates they want, saving bandwidth and improving efficiency.

How do you specify filters in a GraphQL subscription?

A By adding arguments to the subscription field

B By changing the query type

C By using fragments

D By modifying the schema directly

Filters are passed as arguments to the subscription field to control which updates are sent.

If you subscribe to all messages without filtering, what happens?

A You get all messages, even unwanted ones

B You get no messages

C You get only the latest message

D The subscription fails

Without filters, the client receives every update, which may include irrelevant data.

Which of these is a valid reason to use subscription filtering?

A To disable subscriptions

B To increase server load

C To reduce network traffic

D To send duplicate data

Filtering reduces the amount of data sent, lowering network traffic.

What does the server do when a subscription filter condition is not met?

A It closes the subscription

B It sends the update anyway

C It sends an error

D It does not send the update to that client

The server only sends updates that match the filter conditions for each client.

Explain how subscription filtering works in GraphQL and why it is useful.

Think about how you might want only certain messages in a chat app.

Describe a simple example of subscription filtering with a chat room ID.

Imagine subscribing to messages from one chat room, not all rooms.