InjectionToken: Nest can't resolve dependencies

Question

I have a CheckModule which accepts configuration in the forRoot method using a constant CHECK_OPTIONS:

@Module({})
export class CheckModule {
  static forRoot(options?: CheckOptions): DynamicModule {
    return {
      module: CheckModule,
      providers: [
        {
          provide: CHECK_OPTIONS,
          useValue: options,
        },
        CheckService,
      ],
      exports: [CheckService],
    };
  }
}

My CheckService uses the options:

@Injectable()
export class CheckService {
  ...

  constructor(@Inject(CHECK_OPTIONS) options: CheckOptions) {}

  ...

Whenever I debug the application, everything is working fine. But, once I build for production and serve it on Heroku I get an error.

# Production build
nx build $PROJECT_NAME --prod

# Serving the app
node dist/apps/worker/main.js

I get an error:

ERROR [ExceptionHandler] Nest can't resolve dependencies of the CheckService (?). Please make sure that the argument CHECK_OPTIONS at index [0] is available in the CheckModule context.

Am I missing something here? I'm kind of clueless...

Answer 1

In my app.module I imported the CheckModule as:

imports: [
  CheckModule.forRoot(),
  ...
]

This method had an optional parameter for CheckOptions:

forRoot(options?: CheckOptions) { ... }

However my CheckService expects a CHECK_OPTIONS which is not optional. This is what caused the error. Correctly marking this InjectionToken as @Optional() resolved this issue.

So, I've changed the code from:

  constructor(@Inject(CHECK_OPTIONS) options?: CheckOptions) {}

To:

  constructor(@Optional() @Inject(CHECK_OPTIONS) options?: CheckOptions) {}
              ^^^^^^^^^^^

See https://docs.nestjs.com/providers#optional-providers for more information about the @Optional() decorator.