How do you create a multi-provider pattern in NestJS to inject multiple implementations for the same token?

Q: How do you create a multi-provider pattern in NestJS to inject multiple implementations for the same token?

export interface Notifier { send(message: string): Promise ; } @Injectable() export class EmailNotifier implements Notifier { async send(msg: string) {} } @Injectable() export class SmsNotifier implements Notifier { async send(msg: string) {} } @Injectable() export class PushNotifier implements Notifier { async send(msg: string) {} } // Aggregate all into a single array token { provide: 'NOTIFIERS', useFactory: ( email: EmailNotifier, sms: SmsNotifier, push: PushNotifier, ): Notifier[] => [email, sms, push], inject: [EmailNotifier, SmsNotifier, PushNotifier], } // Inject and iterate @Injectable() export class NotificationService { constructor(@Inject('NOTIFIERS') private notifiers: Notifier[]) {} async notifyAll(message: string) { await Promise.all(this.notifiers.map(n => n.send(message))); } } Adding a new notifier only requires registering it as a provider and adding it to the factory — no changes to NotificationService. Each implementation is a singleton provider and can inject its own dependencies. The array token is easy to mock in tests with a simple useValue array. Works for any interface-based polymorphism scenario: validators, event handlers, middleware chains.

Difficulty: 5/10

custom providers, dependency injection, multi-token injection

NestJS does not natively support multi-providers like Angular, but the same result is achieved with a factory provider that aggregates all implementations into an array or map and exposes them under a single token.

Multi-provider pattern using a factory

Advantages of this approach:

1
Adding a new notifier only requires registering it as a provider and adding it to the factory — no changes to NotificationService.
2
Each implementation is a singleton provider and can inject its own dependencies.

How do you create a multi-provider pattern in NestJS to inject multiple implementations for the same token?

NestJS does not natively support multi-providers like Angular, but the same result is achieved with a factory provider that aggregates all implementations into an array or map and exposes them under a single token.

Scenario Questions

Follow-up Questions