NestJs: inject service (or anything) into imported module - dependency-injection

Question

Is there a way better than below to inject a service or component inside an imported module?
export interface AmqpInterceptor{
after(message:any):Promise<void>;
}
export class AmqpInterceptors extends Array<AmqpInterceptor>{
}
//generic library module
#Module({
providers:[{
provide: AmqpInterceptors,
useValue: []
}]
}
export class AMQPModule implements OnModuleInit{
static register(options: AMQPOptions): DynamicModule {
const providers = options.providers || []
return {
module: AMQPModule,
providers: [
...providers,
OtherProvider
]
}
}
}
//end user module
#Module({
imports: [
AMQPModule.register(({
// I had to create a factory method to pass providers as an argument.
// I would think that it is not a good practice
providers: [{
provide:AmqpInterceptors,
useValue:[MyCustomInterceptor]
}]
})
],
providers: [
]
})
export class QueueModule {
}
Current working solution: I declare a default empty array in the generic module and a factory method that allows to pass custom value in module construction.(In my happiest world I declare multiple instances of an interface and then, DI collects all of these, but I thinks this is really impossible in NestJs)

Answer 1

you can use a package like #golevelup/nestjs-discovery to help you with.
Basically you've to do the following:
// AMQP Module
// amqp-interceptor.decorator.ts
import { SetMetadata } from '#nestjs/common';
export function AmqpInterceptor() {
return SetMetadata('AMQP_INTERCEPTOR', true)
}
// amqp-explorer.ts
import { OnModuleInit } from '#nestjs/common'
#Injectable()
export class AmqpExplorer implements OnModuleInit {
constructor(
private readonly discoveryService: DiscoveryService,
) {}
async onModuleInit(): Promise<void> {
const amqpInterceptorProviders = await this.discoveryService.providers('AMQP_INTERCEPTOR')
// you can store this list, to be queried by some
// other provider to use interceptors, etc.
}
}
// amqp.module.ts
#Module({ providers:[AmqpExplorer]})
export class AMQPModule { }
// end user module
// end-user.module.ts
#Module({ imports:[AMQPModule], providers: [SomeAmqpInterceptor] })
export class EndUserModule { }
// some-amqp.interceptor.ts
#Injectable()
#AmqpInterceptor()
export class SomeAmqpInterceptor {
run(): void { console.log('intercepting') }
}
Obs:
Interceptor decorator: you can add any params which would help you to improve your api
I suggest this (list of providers) instead of injecting decorated providers into your module, because I don't know how do you plan to use them. This way, you've a list of providers and can invoke each one.
AMQP_INTERCEPTOR string can collide with some other metadata, it's a good practice add something more specific to avoid two metadata with same one in a module
To invoke the interceptors later:
import { ExternalContextCreator } from '#nestjs/core/helpers/external-context-creator'
export class Runner {
constructor(
private readonly handler: DiscoveredMethodWithMeta,
private readonly externalContextCreator: ExternalContextCreator,
) { }
run(): void {
const handler = this.externalContextCreator.create(
this.handler.discoveredMethod.parentClass.instance,
this.handler.discoveredMethod.handler,
this.handler.discoveredMethod.methodName,
)
const handlerResult = await handler(content)
}
Didn't run local, but I think this is a good way to start