Real-Time GraphQL with Subscriptions Quiz Quiz

Explore fundamental concepts of real-time GraphQL with this quiz focused on Subscriptions, event-driven architecture, and related protocols. Enhance your understanding of how GraphQL enables dynamic data updates and live communication between clients and servers.

1. Subscription Basics

   In the context of GraphQL, what is the primary purpose of using a Subscription operation?

   1. To perform batch mutations in one request
   2. To fetch static data without changes
   3. To receive real-time updates from the server as data changes
   4. To send multiple queries simultaneously

   Explanation: Subscriptions are designed to provide real-time communication by pushing updates from the server to the client whenever specific data changes. Unlike queries, which only fetch data once, subscriptions create a persistent connection for ongoing updates. Sending multiple queries simultaneously does not require subscriptions and is managed differently. Fetching static data would simply use a query, and mutations manage changes but do not provide ongoing updates.

2. Underlying Protocols

   Which communication protocol is most commonly used to establish and maintain real-time GraphQL subscriptions?

   1. gRPC
   2. WebSockets
   3. HTTP POST
   4. FTP

   Explanation: WebSockets enable two-way communication between client and server, making them ideal for real-time applications like GraphQL subscriptions. While HTTP POST is used for one-off requests, it does not support persistent connections required for subscriptions. gRPC is another communication protocol but is not standard for GraphQL subscriptions. FTP is unrelated and used for file transfers, not real-time data exchange.

3. Event Filtering

   How can a client ensure it only receives specific kinds of events, such as new comments on a particular post, using a GraphQL subscription?

   1. By including arguments in the subscription operation to filter events
   2. By subscribing to all events and filtering on the client side only
   3. By limiting the payload size in the subscription query
   4. By using a GET request instead of a POST request

   Explanation: Clients can include arguments in subscription operations to tell the server which events they are interested in, such as specifying a post ID to receive only relevant comments. Using GET requests does not control event filtering. Limiting payload size relates to network optimization but does not affect event selection. Although filtering on the client side is possible, it is inefficient compared to server-side filtering via arguments.

4. Subscription Lifecycle

   What typically happens when a client unsubscribes from a real-time GraphQL subscription, such as closing a chat window?

   1. The server closes the connection and stops sending updates for that subscription
   2. The client receives older, cached data instead of new events
   3. The server automatically sends a summary of missed messages
   4. The client switches to polling for updates over HTTP

   Explanation: When a client unsubscribes, the server is notified to stop sending further updates for that subscription and releases any associated resources. Receiving cached data is unrelated to subscription termination. Sending a summary of missed messages is not standard behavior. Switching to HTTP polling would only occur if the application is explicitly designed to do so, not as default subscription behavior.

5. Comparison with Queries

   How does the data delivery mechanism of a GraphQL subscription differ from that of a standard query in practice?

   1. Subscriptions provide asynchronous updates as data changes, while queries return a snapshot of data at a single point in time
   2. Queries can only return simple data types, while subscriptions deliver complex objects
   3. Subscriptions use HTTPS exclusively, whereas queries use HTTP only
   4. Subscriptions require manual polling to get updates, unlike queries

   Explanation: With subscriptions, the server pushes data updates to the client asynchronously whenever relevant changes occur. In contrast, a query retrieves the current data once and completes. Subscriptions do not require manual polling; they use push mechanisms. Both queries and subscriptions support complex objects. The use of HTTPS or HTTP depends on server setup and is not exclusive to either operation type.