How to "Join" to subgraphs?

[rawkode]

I have two existing services:

People:

extend type Person @key(fields: "id") {
  id: ID!
  name: String!
}

Shows:

type Show @key(fields: "id") {
  id: ID!
  name: String!
}

I want to add a third, that extends each of these: ShowHosts.
It's job is to extend People with shows() and extend Shows with people()

extend type Person @key(fields: "id") {
  id: ID! @external
  shows: [Show]
}

extend type Show @key(fields: "id") {
  id: ID! @external
  people: [Person]
}

I can't work out what my resolver for this would look like.

Could someone please help me out?

[kamilkisiela]

What GraphQL server are you using for the subgraph?

I will assume it's JS-based like https://the-guild.dev/graphql/yoga-server .

In the resolvers object:

{
  Person: {
    __resolveReference(key: { id: string }) {
      const shows = getShowsOfPerson(key.id);
      
      if (shows == null) { return null }
      
      return { id: key.id, shows };
      // if you prefer, you can also return `{ id }` and add `shows` function to the object (Person.shows()).
    }
  }
}

[rawkode]

Thanks