EventSubscriber not Singleton

[World3Developer]

I am using Mikro-orm with NestJS.
I am trying to do a class that EventSubscriber like in documentation:

This is my groups.module.ts, where I import GroupsSubscriber:

import { Module } from '@nestjs/common';
import { MikroOrmModule } from '@mikro-orm/nestjs';
import { GroupEntity } from './entities/group.entity';
import { GroupsService } from './groups.service';
import { GroupsController } from './groups.controller';
import { PassportModule } from '@nestjs/passport';
import { GroupsSubscriber } from './groups.subscriber';

@Module({
  imports: [
    MikroOrmModule.forFeature([GroupEntity]),
    PassportModule.register({ defaultStrategy: 'jwt' }),
  ],
  controllers: [GroupsController],
  providers: [GroupsService, GroupsSubscriber],
  exports: [GroupsService],
})
export class GroupsModule {}

And, this is my GroupsSubscriber, that implements EventSubscriber.

import {
  EntityName,
  EventArgs,
  EventSubscriber,
  Subscriber,
} from '@mikro-orm/core';
import { GroupEntity } from './entities/group.entity';
import { GroupsService } from './groups.service';

@Subscriber()
export class GroupsSubscriber implements EventSubscriber<GroupEntity> {
  constructor(private groupsService: GroupsService) {
    console.log('TEST');
    setInterval(() => {
      console.log('A: ', this.groupsService);
    }, 1000);
  }

  getSubscribedEntities(): EntityName<GroupEntity>[] {
    return [GroupEntity];
  }

  async afterCreate(args: EventArgs<GroupEntity>): Promise<void> {
    console.log('groupsService: ', this.groupsService);
  }
}

The error is that I think that I have two instances from this class, because the output of the console is:

A:  undefined
A:  GroupsService {
  groupRepository: MongoEntityRepository {
    _em: [EntityManager<1>],
    entityName: 'GroupEntity'
  }
}
A:  undefined
A:  GroupsService {
  groupRepository: MongoEntityRepository {
    _em: [EntityManager<1>],
    entityName: 'GroupEntity'
  }
}
A:  undefined
A:  GroupsService {
  groupRepository: MongoEntityRepository {
    _em: [EntityManager<1>],
    entityName: 'GroupEntity'
  }

[B4nan]

The ORM instantiates subscribers only once when the @Subscriber() decorator gets evaluated, which happens only once unless you clear the require cache, so if that happens multiple times, it's probably something in your setup, rather than in this package. In latest version, even cloning the EventManager uses the exact same subscriber instances.

Note that you can as well pass the subscribers via ORM config - there you provide the instances yourself, and you don't use the @Subscriber() decorator, so it's definitely one way to get around it.

[World3Developer]

Well, it's possible that when NestJS do the import of the modules, may be that nest calls two times this constructor:

[16:32:52] Starting compilation in watch mode...

[16:32:57] Found 0 errors. Watching for file changes.

TEST
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [NestFactory] Starting Nest application...
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] AppModule dependencies initialized +93ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] PusherModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] PassportModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] ThrottlerModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] HttpModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] TestModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] DiscoveryModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] ConfigHostModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] ScheduleModule dependencies initialized +2ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] ConfigModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] JwtModule dependencies initialized +10ms
[Nest] 31543  - 02/01/2023, 16:32:58     LOG [InstanceLoader] AuthModule dependencies initialized +3ms
A:  undefined
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmCoreModule dependencies initialized +1716ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MikroOrmModule dependencies initialized +0ms
TEST
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] NewsModule dependencies initialized +4ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] TransactionsModule dependencies initialized +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] RewardsModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] MarketplaceModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] NotificationsModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] ReferralsModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] GridsModule dependencies initialized +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] UsersModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] BanksModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] GroupsModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [InstanceLoader] CellsModule dependencies initialized +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] UsersController {/api/users}: +101ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/users, GET} route +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/users/me, GET} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/users/userAndBank, GET} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/users/:id, GET} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/users/:id, PATCH} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] AuthController {/api/auth}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/auth, POST} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] ReferralsController {/api/referrals}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/referrals/me, GET} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] BanksController {/api/banks}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/banks/me, GET} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] TransactionsController {/api/banks/transactions}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/banks/transactions, GET} route +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/banks/transactions/me, GET} route +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/banks/transactions/:id, GET} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] RewardsController {/api/referrals/rewards}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/referrals/rewards/me, GET} route +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/referrals/rewards/addReward, GET} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] NotificationsController {/api/notifications}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/notifications/createForOneUser, POST} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/notifications, GET} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] NewsController {/api/news}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/news/visibleNews, GET} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] MarketplaceController {/api/marketplace}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/marketplace/addItem, POST} route +3ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] GridsController {/api/grids}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/grids/create, POST} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] CellsController {/api/grids/cells}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/grids/cells/getCellsInfo, POST} route +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/grids/cells/buyCells, POST} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/grids/cells/getCellsInBB, POST} route +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] GroupsController {/api/groups}: +1ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/groups, GET} route +3ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RoutesResolver] TestController {/api/test}: +0ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [RouterExplorer] Mapped {/api/test/test1, GET} route +2ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG [NestApplication] Nest application successfully started +14ms
[Nest] 31543  - 02/01/2023, 16:33:00     LOG 🚀 Application is running on: http://localhost:3333/api
A:  undefined
A:  GroupsService {
  groupRepository: MongoEntityRepository {
    _em: [EntityManager<1>],
    entityName: 'GroupEntity'
  }

Take a look to the TEST word. Appears two times, once at the top, and one in the middle of the boot. I can avoid that, or I don't know how to do it.

Then, I am trying to do using:

MikroORM.init({
  subscribers: [new GroupSubscriber()],
});

without using the @subscriber decorator.

But, then, I can not inject the service in the Subscriber, because the subscriber has a service injected, and it wants to I inject when I put it in the init method.

What am I doing wrong? Or have I misconception? May be that I can not inject a service in the constructor of a EventSubscriber?

[B4nan]

Well, it's possible that when NestJS do the import of the modules, may be that nest calls two times this constructor:

Nest does not call the constructor, the decorator function does, and those are executed only once per the file execution.

But, then, I can not inject the service in the Subscriber,

Oh ok, I missed that, that's the problem - you either register it as a nest service and let nest DI instantiate it, or let the ORM do it through the @Subscriber() decorator, or you do it explicitly and pass in the subscriber instance via ORM config. You can't combine those approaches.

[B4nan]

https://mikro-orm.io/docs/usage-with-nestjs#using-eventsubscriber

[World3Developer]

I missed the @Injectable decorator. Sorry.

I finally imported in a provider using @Injectable decorator and I have only one instance with access to the service.

Thanks a lot for your help.