How do you map PubSub value of a GraphQL subscription in Apollo?

Question

I'm making a GraphQL backend in Apollo, and I'd like to use subscriptions. I followed Apollo's docs, and I've gotten basic subscriptions working using graphql-subscriptions. This package also comes with filtering via the built-in withFilter function. However, I don't want to emit all of the data published via PubSub because some of this data is used for filtering purposes only.

Ex.

// GraphQL Schema
type Subscription {
  mySubscription(filter: MySubscriptionFilter!): ID!
}

// Publishing the event
pubsub.publish("MY_SUBSCRIPTION", { id: "2092330", username: "asdf", roles: [ "USER", "MODERATOR" ] });

// Handling the event for a subscription
const resolvers = {
  Subscriptions: {
    mySubscription: {
      subscribe: withFilter(
        () => pubsub.asyncIterator("MY_SUBSCRIPTION"),
        (payload, variables) => {
          return customFiltering(payload, variables);
        }
      )
    }
  }
}

This returns an object with the type: { id, username, roles }. However, the username and roles fields are only used for filtering. I ultimately need to return an object of type { mySubscription: id }, because that's what my GraphQL schema says.

Is there a way to do something like this?

// Handling the event for a subscription
const resolvers = {
  Subscriptions: {
    mySubscription: {
      subscribe: withFilter(
        () => pubsub.asyncIterator("MY_SUBSCRIPTION"),
        (payload, variables) => {
          return customFiltering(payload, variables);
        }
      ).map(x => {
        return { mySubsription: x.id }
      }) // Map function where x is the payload from the pubsub
    }
  }
}

score 0 · Accepted Answer · answered Jun 15 '22 at 19:47

Whoops, it looks like I overlooked the resolve function in a subscription.

From the graphql-subscriptions github page

Payload Manipulation

You can also manipulate the published payload, by adding resolve methods to your subscription:

const SOMETHING_UPDATED = 'something_updated';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      resolve: (payload, args, context, info) => {
        // Manipulate and return the new value
        return payload.somethingChanged;
      },
      subscribe: () => pubsub.asyncIterator(SOMETHING_UPDATED),
    },
  },
}

How do you map PubSub value of a GraphQL subscription in Apollo?

1 Answers1

Payload Manipulation