Subscription error

I’m submitting a…

[ ] Regression 
[ ] Bug report
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead post your question on Stack Overflow.

Current behavior

{
  "error": {
    "message": "Subscription field must return Async Iterable. Received: { pubsub: { ee: [Object], subscriptions: {}, subIdCounter: 0 }, pullQueue: [], pushQueue: [], running: true, allSubscribed: null, eventsArray: [\"onCategory\"] }"
  }
}

Expected behavior

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

  @Subscription(() => [Category])
  public onCategory() {
    return pubSub.asyncIterator('onCategory');
  }

Environment

Nest version: 6.8.2

 
For Tooling issues:
- Node version: v12.11.1  
- Platform:  macOS Catalina

Others:

[rmaes4]

Just stumbled across this and ran into the same issue. My solution was to extend ClassSerializerInterceptor and basically have it apply to everything except GQL subscriptions. This way I won’t have to manually add decorators all around my code base minus subscription resolvers and instead I can register it as a global interceptor.

my-class-serializer.interceptor.ts

import {
  CallHandler,
  ClassSerializerInterceptor,
  ExecutionContext,
  Injectable
} from '@nestjs/common';
import { Observable } from 'rxjs';

@Injectable()
export class MyClassSerializerInterceptor extends ClassSerializerInterceptor {
  constructor(protected readonly reflector: any) {
    super(reflector);
  }
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    if ((context.getType() as string) === 'graphql') {
      const op = context.getArgByIndex(3).operation.operation;
      if (op === 'subscription') {
        return next.handle();
      }
    }
    return super.intercept(context, next);
  }
}

And register it like so

main.ts

...
app.useGlobalInterceptors(
    new MyClassSerializerInterceptor(app.get(Reflector))
  );
...

[Simolation]

It works when excluding all subscriptions from the serializer, but what if I want the response to be serialized? I have fields which need to be transformed, but I can’t do that as the serializer tries to transform the AsyncIterable. When doing the serialization in resolve it does work, but how do I serialize additional resolved values which are not included in the data which is transported over the PubSub?