Subscriptions and interfaces

[theogravity]

I am currently porting over a subscription from our apollo server to giraph. We have a single resolver for our subscription, which can emit different kinds of events, which all implement an interface.

It looks something like this:

export class BaseSampleEvent {
  id: string;

  constructor(id: string) {
    this.id = id;
  }
}

builder.interfaceType(BaseSampleEvent, {
  name: 'IBaseSampleEvent',
  fields: (t) => ({
    id: t.exposeID('id'),
  }),
});

export class NewUserEvent extends BaseSampleEvent {
   ...
}

builder.objectType(NewUserEvent, {
  name: 'NewUserEvent',
  interfaces: [BaseTeamEvent],
  isTypeOf: (value) => value instanceof NewUserEvent,
  fields: (t) => ({
    id: t.exposeID('id'),
  }),
});

builder.subscriptionField('sampleEvents', (t) => {
  return t.field({
    type: BaseSampleEvent
    subscribe: () => {
       // from graphql-subscriptions lib
       return withFilter(...)()
    },
    resolve: (payload) => payload as BaseSampleEvent
  })
})

When I attempt to publish the NewUserEvent event, I get the following error:

ERROR 20:17:8.51 Abstract type "IBaseSampleEvent" must resolve to an Object type at runtime for field "Subscription.sampleEvents" with value { ... } Either the "sampleEvents" type should provide a "resolveType" function or each possible type should provide an "isTypeOf" function.\n    at ensureValidRuntimeType 

Not sure what I'm doing wrong here as I do have isTypeOf defined. In our apollo implementation, we did have to define a set of mapped resolvers / types for BaseSampleEvent, and the closest thing I'm seeing with this is to use a giraphql union, and assign that union as the return type of the subscription.

If that is the case, do I need the isTypeOf on the builder.objectType(NewUserEvent) event objects themselves?

[hayes]

Are your events actually instances of the classes you are defining, or are they just objects with the same properties?

[hayes]

I think you would see this error if all your isTypeOf functions are returning false

[hayes]

I think isTypeOf can actually be optional too because the default is an instanceof check when you use a class as the type ref

[theogravity]

They're actually instances of the classes. It seems I can't remove isTypeOf without removing the interfaces property. If I remove both, the event types do not implement anything in the generated schema.

But, I think I figured out what's going on. I noticed this behavior too when it came to writing the subscribe function in our apollo server.

The value passed to isTypeOf is serialized to an object. When I console.logged out the event in isTypeOf, it was a pure object. I wonder if the serialization is a native gql thing or specific to the pubsub lib being used.

We actually add in an eventType property in our events, and so when I compared that property, it works!

  isTypeOf: (value) => {
    return value.eventType === EventType.NewUserEvent;
  },

[hayes]

I think it must be a pub-sub thing. I know gql won't automatically serialize it. Probably to standardize behavior across different implementations (in prod most people will use something like redis, which would cause there data to be serialized, so serialization would make things consistent for an in-process implementation)