Hello friends!
I'm glad to present the library for NestJS. In my article I showed an approach how we can implement transport-eventbus for nestJS but now we can use a done library for it. Go!
nestjs-transport-eventbus allows broadcasting events via variety of nestjs trasports in easy way
Installation
npm i nestjs-transport-eventbus
Quick Start
Import TransportEventBusModule into a willing module, example below:
import { TransportEventBusModule } from 'nestjs-transport-eventbus';
@Module({
imports: [
TransportEventBusModule
],
controllers: [AppController],
providers: [
AppService
],
})
export class AppModule {
}
TransportEventBusModule applies two arguments:\
publishers - array of transport publishers which are based on ClientProxy\
providers - the additional providers for module
Example with RabbitMQ(RabbitPublisher)
For creating a transport publisher there is enough to implement the following steps:
1 Implement RabbitPublisher, example below:\
import { Injectable } from '@nestjs/common';
import { ClientProxy, Transport, Client} from '@nestjs/microservices';
import { Publisher } from 'nestjs-transport-eventbus';
@Injectable()
@Publisher(Transport.RMQ)//Choose the appropriate type of transport in this case `RMQ`
export class RabbitPublisher {
@Client({
transport: Transport.RMQ,
options: {
urls: ['amqp://rabbit:rabbit@rabbitmq:5672'],
queue: 'event_service_queue',
queueOptions: {
durable: true,
},
},
})
client: ClientProxy;
}
2 Inject RabbitPublisher into TransportEventBusModule, example below:
import { Module } from '@nestjs/common';
import { TransportEventBusModule } from 'nestjs-transport-eventbus';
import { RabbitPublisher } from '...';
@Module({
imports: [
TransportEventBusModule.forRoot({
publishers: [RabbitPublisher]
})
],
controllers: [],
providers: [
],
})
export class AppModule {
}
3 Create an event for publisher, example below:
import { TransportType, ExcludeDef } from 'nestjs-transport-eventbus';
import { Transport } from '@nestjs/microservices';
@TransportType(Transport.RMQ)//can apply array of transports, for example RMQ,REDIS
export class RabbitEvent {
constructor(
readonly message: string
) {
}
}
Notice: By default, events are handling on both sides broadcasting server and receiving server, for changing this situation add
@ExcludeDef()declaration,
can look like below:....
@TransportType(Transport.RMQ)
@ExcludeDef()
export class RabbitEvent
...
4 Inject TRANSPORT_EVENT_BUS_SERVICE, example below:
import { Inject, Injectable } from '@nestjs/common';
import { TRANSPORT_EVENT_BUS_SERVICE } from 'nestjs-transport-eventbus';
import { IEventBus } from '@nestjs/cqrs';
import { DefaultEvent } from '...';
import { RabbitEvent } from '...'
@Injectable()
export class AppService {
constructor(
@Inject(TRANSPORT_EVENT_BUS_SERVICE) private readonly eventBus: IEventBus
){
}
rabbitEvent(): void {
this.eventBus.publish(new RabbitEvent('Pass some param'));
}
}
Notice: Events via AggregateRoot
import { CommandHandler, EventPublisher, ICommandHandler } from '@nestjs/cqrs';
import { TryAggregateRootCommand } from '...';
import { Inject } from '@nestjs/common';
import { TRANSPORT_EVENT_BUS_PUBLISHER } from 'nestjs-transport-eventbus';
import { TestModel } from '...';
@CommandHandler(TryAggregateRootCommand)
export class TryAggregateRootCommandHandler implements ICommandHandler<TryAggregateRootCommand> {
constructor(
@Inject(TRANSPORT_EVENT_BUS_PUBLISHER) private readonly publisher: EventPublisher
) {
}
async execute(command: TryAggregateRootCommand) {
const {message} = command;
const aggregator = this.publisher.mergeObjectContext(
new TestModel()
);
aggregator.applyEvent(message);
aggregator.commit();
}
}
5 For handling the broadcasted event on receiving side can look like the following:
import { Controller, Inject } from '@nestjs/common';
import { EventPattern } from '@nestjs/microservices';
import { TRANSPORT_EVENT_BUS_PATTERN, TRANSPORT_EVENT_BUS_SERVICE, TransportEvent } from 'nestjs-transport-eventbus';
import { IEvent, IEventBus } from '@nestjs/cqrs';
@Controller()
export class AppService {
constructor(
@Inject(TRANSPORT_EVENT_BUS_SERVICE) private readonly eventBus: IEventBus
){
}
@EventPattern(TRANSPORT_EVENT_BUS_PATTERN)
handle(@TransportEvent() event: IEvent): void {
this.eventBus.publish(event);
}
Notice:
TRANSPORT_EVENT_BUS_PATTERN- can pass via .env
Examples
Example is presented two services which communicate with each other via RabbitMQ
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