为什么我不能在构造函数中使用我的 nestjs 自定义装饰器？

Question

I want to create a custom decorator to return tenant information. I have the following code:

export type TenantInfo = {
    token: string
    id: string
}

export const TenantInfo = createParamDecorator(
  (data: unknown, context: ExecutionContext): TenantInfo => {
      // todo use context to get from auth header
      return { id: '1', token: 'todo' }
  },
);

Now i register it in the tenant service:

@Injectable({ scope: Scope.REQUEST })
export class TenantService {
  private readonly _tenantInfo: TenantInfo;

  constructor(
    @TenantId() tenantInfo: TenantInfo,
  ) {
    this._tenantInfo = tenantInfo;
    logger.log(`Received GRPC message from tenant id ${tenantInfo.id}`);
  }
}

And when I run my code it says:

Error: Nest can't resolve dependencies of the TenantService (?). Please make sure that the argument Object at index [0] is available in the TenantModule context.

Potential solutions:

• If Object is a provider, is it part of the current TenantModule?
• If Object is exported from a separate @Module, is that module imported within TenantModule? @Module({ imports: [ /* the Module containing Object */ ]

I'm not sure how to get around this. It's saying register it in the module but I get errors if I try putting TenantInfo in the providers array...

Type '(...dataOrPipes: unknown[]) => ParameterDecorator' is not assignable to type 'Provider'

How do you do this? All I want is to get some details from the request context.

Answer 1

createParamDecorator only creates decorators that work for route handlers (Controllers, Resolvers, or Gateways). For something that can be injected at the constructor level of a service you can either inject the request, via @Inject(REQUEST) , or you can create a custom request scoped provider and custom decorator like so:

export const InjectTenantId = () => Inject('TENANTID');

export const tenantIdProvider = {
  provide: 'TENANTID',
  inject: [REQUEST],
  scope: Scope.REQUEST,
  useFactory: (request) => getTenantIdFromRequest(request)
}

And now in your constructor you can do @InjectTenantId() private readonly tenantInfo: TenantInfo .