Modify response with nestjs interceptor

Question

I have Interceptor for modify icon path like this:

@Injectable()
export class GetProgramIconInterceptor implements NestInterceptor {
    intercept(context: ExecutionContext, next: CallHandler<any>): Observable<any> | Promise<Observable<any>> {
        return next.handle().pipe(
            map(data => {
                return {
                    ...data,
                    icon: generalFUnctions.getApplicationIcon(data.icon)
                };
            }),
        );
    }
}

and when I use this in my find method, it works correctly and modifies the icon path.

@UseInterceptors(GetProgramIconInterceptor)
async find(id: string): Promise<Application> {
    const application = await this.repository.findById(id);
     if (!application) throw new ApplicationNotFoundException();
     return application;
}

and when I use this Interceptor to the findAll method it doesn't work correctly and doesn't modify the path.

@UseInterceptors(GetProgramIconInterceptor)
async findAll(): Promise<Application[]> {
     return this.repository.find();
}

I know the result of the findAll method is an array and I can create another Interceptor for it. Is there any way to handle it with one Interceptor

Answer 1

Since you are working with promises (And not already observable) results from the repository model functions ( find and findById ) when piping into the observable it means you are observing over repository or repository[]

Attaching a codesandbox of an example i have created mapping over resource that is possibly single object or array of objects.

The magic here is just making sure we have a conditional expression for when the resource is array or not

map((repositoryOrRespositories) => {
  if (Array.isArray(repositoryOrRespositories)) {
    return item.map((repository) => ({
      ...repository,
      icon: generalFUnctions.getApplicationIcon(repository.icon)
    }));
  } else {
    return { ...repositoryOrRespositories, icon: generalFUnctions.getApplicationIcon(repositoryOrRespositories.icon) };
  }
})

If the results from the repository model were observables you had to use iif expressions from rxjs.