Event patterns (event-based) in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an event handler using the correct decorator.

NestJS

import { Controller } from '@nestjs/common';
import { EventPattern } from '@nestjs/microservices';

@Controller()
export class AppController {
  @[1]('order_created')
  handleOrderCreated(data: any) {
    console.log('Order created event received:', data);
  }
}

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

ASubscribeMessage

BEventPattern

CMessagePattern

DOnEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Using @MessagePattern instead of @EventPattern

Using @SubscribeMessage which is for WebSocket events

Using @OnEvent which is for internal event emitter

The @EventPattern decorator is used in NestJS to listen for specific events in event-based communication.

2fill in blank

medium

Complete the code to emit an event named 'user_registered' with user data.

NestJS

import { ClientProxy } from '@nestjs/microservices';

export class UserService {
  constructor(private client: ClientProxy) {}

  registerUser(user: any) {
    // user registration logic
    this.client.[1]('user_registered', user);
  }
}

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Asend

Bpublish

Cdispatch

Demit

Attempts:

3 left

💡 Hint

Common Mistakes

Using send which expects a response

Using publish which is not a ClientProxy method

Using dispatch which does not exist

The emit method on ClientProxy is used to send events to the event bus in NestJS.

3fill in blank

hard

Fix the error in the event handler method signature to properly receive event data.

NestJS

import { Controller } from '@nestjs/common';
import { EventPattern } from '@nestjs/microservices';

@Controller()
export class PaymentController {
  @EventPattern('payment_processed')
  handlePayment([1]) {
    console.log('Payment processed:', data);
  }
}

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Adata

Bevent

Cpayload

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name different from what is used inside the method

Not defining any parameter to receive event data

The event handler method should receive the event data as a parameter, commonly named data.

4fill in blank

hard

Fill both blanks to create a service that listens to 'inventory_updated' events and logs the update.

NestJS

import { Injectable } from '@nestjs/common';
import { [1] } from '@nestjs/microservices';

@Injectable()
export class InventoryService {
  @[2]('inventory_updated')
  handleInventoryUpdate(update: any) {
    console.log('Inventory updated:', update);
  }
}

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AEventPattern

BMessagePattern

CSubscribeMessage

DOnEvent

Attempts:

3 left

💡 Hint

Common Mistakes

Importing and using different decorators

Using MessagePattern which is for request-response

Both the import and the decorator should be EventPattern to listen to event-based messages.

5fill in blank

hard

Fill all three blanks to create a client service that emits 'notification_sent' events with a message payload.

NestJS

import { Injectable } from '@nestjs/common';
import { [1] } from '@nestjs/microservices';

@Injectable()
export class NotificationService {
  constructor(private client: [2]) {}

  sendNotification(message: string) {
    this.client.[3]('notification_sent', { message });
  }
}

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AClientProxy

Cemit

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'send' instead of 'emit' for events

Mismatching injected client type and import

The ClientProxy is imported and injected to emit events using the emit method.