What is ModuleRef in NestJS and when would you use it?

Q: What is ModuleRef in NestJS and when would you use it?

@Injectable() export class AppService { constructor(private moduleRef: ModuleRef) {} async getService(type: string) { if (type === 'singleton') { // Resolves singleton provider return this.moduleRef.get(UsersService); } // Resolves a scoped/transient provider in its own DI context return await this.moduleRef.resolve(RequestScopedService); } } Strategy pattern — dynamically choose which provider to use at runtime. Lazy initialization — resolve a heavy provider only when first needed. Factory services — create instances of transient providers on demand. moduleRef.get() is synchronous and only works for singleton providers. moduleRef.resolve() is async and creates a new DI sub-context for scoped providers.

Difficulty: 5/10

dynamic provider resolution, runtime dependency injection, module ref usage

ModuleRef is a reference to the current module's DI container. Inject it to resolve providers imperatively at runtime — useful when you need a provider conditionally or need to retrieve a transient/request-scoped provider dynamically. Use moduleRef.get() for singletons and moduleRef.resolve() for scoped providers.

Using ModuleRef to resolve providers dynamically

Common use cases:

1
Strategy pattern — dynamically choose which provider to use at runtime.
2
Lazy initialization — resolve a heavy provider only when first needed.
3
Factory services — create instances of transient providers on demand.
4
moduleRef.get() is synchronous and only works for singleton providers.
5
moduleRef.resolve() is async and creates a new DI sub-context for scoped providers.

Scenario Questions

0-2 years experience

1You need to get an instance of a service inside a NestJS guard, but you can't inject it via the constructor. How would you use ModuleRef to retrieve it?
2If you call moduleRef.get(MyService, { strict: false }) and the provider isn't registered, what will happen at runtime?
3What would be the result of requesting a request‑scoped provider using ModuleRef from within a singleton?

Follow-up Questions

What are the risks of using ModuleRef inside a singleton service?
How does the 'strict' flag change the behavior of ModuleRef.get?
In what ways does ModuleRef improve or hurt testability compared to @Inject?