prisma2 subscriptions returns data: null

I have a basic pubsub working here using the boilerplate and graphql-yoga: https://github.com/ryanking1809/prisma2_subscriptions https://codesandbox.io/s/github/ryanking1809/prisma2_subscriptions/tree/sql-lite

With a publish mutation:

const Mutation = objectType({
  name: 'Mutation',
  definition(t) {
   //...
    t.field('publish', {
      type: 'Post',
      nullable: true,
      args: {
        id: idArg(),
      },
      resolve: async (parent, { id }, ctx) => {
        const post = await ctx.photon.posts.update({
          where: { id },
          data: { published: true },
          include: { author: true }
        });
        ctx.pubsub.publish("PUBLISHED_POST", {
          publishedPost: post
        });
        return post
      },
    })
  },
})

And a subscription - I'm just returning true to make sure withFilter (from graphql-yoga) is working.

const Subscription = objectType({
    name: "Subscription",
    definition(t) {
        t.field("publishedPostWithEmail", {
            type: "Post",
            args: {
                authorEmail: stringArg({ required: false })
            },
            subscribe: withFilter(
                (parent, { authorEmail }, ctx) => ctx.pubsub.asyncIterator("PUBLISHED_POST"),
                (payload, { authorEmail }) => true
            )
        });
    }
});

Returning the following on publish (you can copy and paste these into codesandbox - which is neat!)

mutation {
  publish(
    id: "cjzwz39og0000nss9b3gbzb7v"
  ) {
    id,
    title,
    author {
      email
    }
  }
}

subscription {
  publishedPostWithEmail(authorEmail:"prisma@subscriptions.com") {
    title,
    content,
    published
  }
}

{
  "errors": [
    {
      "message": "Cannot return null for non-nullable field Subscription.publishedPostWithEmail.",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "publishedPostWithEmail"
      ]
    }
  ],
  "data": null
}

For some reason, it's returning data: null. When I log payload.publishedPosts in the filter function it seems as though everything is there.

{ id: 'cjzwqcf2x0001q6s97m4yzqpi',
  createdAt: '2019-08-29T13:34:26.648Z',
  updatedAt: '2019-08-29T13:54:19.479Z',
  published: true,
  title: 'Check Author',
  content: 'Do you save the author?',
  author:
   { id: 'sdfsdfsdfsdf',
     email: 'prisma@subscriptions.com',
     name: 'Prisma Sub' } }

Is there something I'm missing?

Finally got it figured out! 🙌

The subscription function needs to be named after the key in the pubsub. So if you have a publish function like the following:

ctx.pubsub.publish("PUBLISHED_POST", {
          publishedPost: post
        });

then you have to name your subscription publishedPost

        t.field("publishedPost", {
            type: "Post",
            args: {
                authorEmail: stringArg({ required: false })
            },
            subscribe: withFilter(
                (parent, { authorEmail }, ctx) =>
                    ctx.pubsub.asyncIterator("PUBLISHED_POST"),
                (payload, { authorEmail }) => payload.publishedPost.author.email === authorEmail
            )
        });

if you name your subscription publishedPostWithEmail then no data is returned

        t.field("publishedPostWithEmail", {
                //...
        });

---

Interestingly, if you have 2 keys

ctx.pubsub.publish("PUBLISHED_POST", {
          publishedPost2: post,
          publishedPost3: post
        });

Then if you name your subscription publishedPost2 then publishedPost3 is ommited from the results.

---

Oddly if you subscribe to 2 messages you get back all the data

ctx.pubsub.publish("PUBLISHED_POST", {
          publishedPost: post,
          publishedPost2: post
        });
        ctx.pubsub.publish("PUBLISHED_POST_X", {
          publishedPostX: post,
          publishedPostY: post
        });

ctx.pubsub.asyncIterator([
                        "PUBLISHED_POST",
                        "PUBLISHED_POST_X"
                    ]),

returns publishedPost, publishedPost2, publishedPostX, publishedPostY

So you can get around the above issue by subscribing to an array with a single item and the name of the subscription becomes irrelevant.

        t.field("publishedPostXYZ", {
            type: "Post",
            args: {
                authorEmail: stringArg({ required: false })
            },
            subscribe: withFilter(
                (parent, { authorEmail }, ctx) =>
                    ctx.pubsub.asyncIterator([
                        "PUBLISHED_POST"
                    ]),
                (payload, { authorEmail }) => {
                    return payload.publishedPost.author.email === authorEmail;
                }
            )
        });

---

So seems like this might be a bug 🤔