Subscription types incompatible with graphql-subscription's PubSub

[sarink]

The latest version of graphql-code-generator has changed the subscribe function return type to AsyncIterable<TResult> | Promise<AsyncIterable<TResult>>;

However, when using apollo's graphql-subscriptions lib, the type returned from their pubsub-engine is AsyncIterator https://github.com/apollographql/graphql-subscriptions/blob/master/src/pubsub-engine.ts#L8

AsyncIterable and AsyncIterator types are incompatible.

Example (this code will throw a type error):

const pubsub = new PubSub();

const typeDefs = gql`
  type Subscription {
    root: String
  }
`

const resolvers: Resolvers = {
  Subscription: {
    root: {
      subscribe: () => {
        // Type 'AsyncIterator<unknown, any, undefined>' is not assignable to type 'AsyncIterable<any> | Promise<AsyncIterable<any>>'.
        return pubsub.asyncIterator('root');
      }
    }
  }
};

What's the recommended workaround for this issue?

[armintan]

I do habe the same problem ... any recommendations?

[Thompson-Jordon]

I also have this same issue.

import { SubscriptionResolvers } from '../../generated/graphql'
import { Context } from '../context'

export const NEW_POINT = 'NEW_POINT'

export const Subscription: SubscriptionResolvers<Context> = {
  newPoint: {
    subscribe: (_,__,context) => context.pubsub.asyncIterator(NEW_POINT)
  },
}

I can get the subscription to work if I alter the Graphql Codegen type file to accept 'AsyncIterator<unknown, any, undefined>' This is not a fix I still need to understand how to get it to work without altering the code manually.

[rustic0la]

#7015 (comment)
This is the discussion about the change that resulted in incompatibility between types mentioned above:
SubscriptionSubscribeFn return type been changed from AsyncIterator<TResult> | Promise<AsyncIterator<TResult>> to AsyncIterable<TResult> | Promise<AsyncIterable<TResult>>. But as graphql-subscriptions considered to be a legacy implementation for subscriptions, the possible solution might be making a patch for the library that could undo the change. More details in the thread

[Urigo]

@mpokrovsky I think graphql-subscriptions 3.0 might be happening soon and I think it includes the changes from @n1ru4l

Could you check if using the current state of their PR solves this issue? apollographql/graphql-subscriptions#250

[Mad-Kat]

In the meantime you could use something like this:

subscribe: () => ({
        [Symbol.asyncIterator]: () => pubsub.asyncIterator<{ numberIncremented: number }>('NUMBER_INCREMENTED'),
      }),

[n1ru4l]

@Mad-Kat This would be a working, but rather an ugly workaround. You should not tailor your code and add overhead for pleasing a library with wrong typings.

I recommend everyone to read through #7015 for a full breakdown of the situation and migrate off graphql-subscriptions or use the mentioned patch-package for fixing the typings.

[maxpain]

Any updates?

[n1ru4l]

I will close this issue as there is nothing wrong within graphql-code-generator.

[loucadufault]

Workaround proposed in above #7197 (comment) with graphql-subscriptions withFilter:

import { withFilter } from 'graphql-subscriptions';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: () => ({
        [Symbol.asyncIterator]: withFilter(
          (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
          (payload, variables: SubscriptionSomethingChangedArgs) => payload.somethingChanged.id === variables.relevantId,
        ),
      }),
    },
  },
}