Subscriptions in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the required module for GraphQL subscriptions in NestJS.

NestJS

import { [1] } from '@nestjs/graphql';

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

ASubscription

BGraphQLModule

CResolver

DQuery

Attempts:

3 left

💡 Hint

Common Mistakes

Importing 'Subscription' instead of 'GraphQLModule'.

Using 'Query' which is for queries, not subscriptions.

The GraphQLModule is imported from @nestjs/graphql to enable GraphQL features including subscriptions.

2fill in blank

medium

Complete the code to define a subscription method in a NestJS resolver.

NestJS

@Subscription()
[1]() {
  return pubSub.asyncIterator('messageAdded');
}

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Asubscribe

Basync

Cresolve

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'async' keyword without 'function' keyword.

Using 'resolve' which is for queries or mutations.

The @Subscription() decorator marks subscription resolver methods. The method returns pubSub.asyncIterator('messageAdded'). Conventionally, the method is named subscribe.

3fill in blank

hard

Fix the error in the subscription setup by completing the missing import.

NestJS

import { PubSub } from '[1]';

const pubSub = new PubSub();

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Aapollo-server-express

B@nestjs/graphql

Cgraphql-subscriptions

Drxjs

Attempts:

3 left

💡 Hint

Common Mistakes

Importing PubSub from '@nestjs/graphql' which does not export it.

Using 'rxjs' which is for reactive programming but not for GraphQL PubSub.

The PubSub class used for subscriptions comes from the graphql-subscriptions package, which provides a simple event pub-sub mechanism.

4fill in blank

hard

Fill both blanks to correctly configure the GraphQLModule for subscriptions in NestJS.

NestJS

GraphQLModule.forRoot({
  installSubscriptionHandlers: [1],
  subscriptions: {
    'graphql-ws': [2]
  }
})

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Atrue

Bfalse

C{}

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting installSubscriptionHandlers to false disables subscriptions.

Using null instead of an object for subscriptions config.

To enable subscriptions, installSubscriptionHandlers must be set to true. The subscriptions option can be configured with an empty object {} to use default settings for 'graphql-ws'.

5fill in blank

hard

Fill all three blanks to create a subscription resolver that publishes a message event.

NestJS

import { Resolver, [1] } from '@nestjs/graphql';
import { PubSub } from 'graphql-subscriptions';

const pubSub = new PubSub();

@Resolver()
export class MessageResolver {
  @[2]()
  messageAdded() {
    return pubSub.asyncIterator('messageAdded');
  }

  async addMessage(content: string) {
    await pubSub.[3]('messageAdded', { messageAdded: content });
  }
}

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

ASubscription

Cpublish

DQuery

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Query' decorator instead of 'Subscription'.

Calling 'subscribe' instead of 'publish' to send events.

The Subscription decorator marks the subscription method. The publish method of pubSub sends events to subscribers.