Gateway does not trigger correct resolvers when subgraphs extend and reuse shared types

[abc-moviestarplanet]

Given the following 2 graphql subgraphs:

Subgraph 1:

  extend type Query {
    users: PageOfUser
  }

  type PageOfUser {
    nodes: [User]
  }

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

Subgraph 2:

  extend type User @key(fields: "id") {
    id: ID! @external
    friends: PageOfUser # <-- this is problematic
  }

  type PageOfUser {
    nodes: [User]
  }

Subgraph 2 has a resolver for friends which always returns some data.

If I run the following query against the Gateway:

query {
  users {
    nodes {
      id
      friends {
        nodes {
          id 
        }
      }
    }
  }
}

The response is:

{
  "data": {
    "users": {
      "nodes": [
        {
          "id": "0",
          "friends": null // should not be null
        },
        {
          "id": "1",
          "friends": null // should not be null
        }
      ]
    }
  }
}

And the friends resolver never triggers.

I can get the data for friends correctly if I manually query subgraph 2 directly like this:

query {
  _entities(representations: [{ __typename:"User", id: 1 }]) {
    ...on User {
      id
      friends {
        nodes {
          id
        }
      }
    }
  }
}

So from what I can understand, the Gateway is not requesting the "friends" data from Subgraph 2.

Now if in Subgraph 2 I rename the type PageOfUser to PageOfFriends (a name that is different from that defined in Subgraph 1) then it works fine through the Gateway.

According to this https://www.apollographql.com/docs/federation/v1/value-types/, it is fine for the subgraphs to define the same types multiple times, as long as they are exactly identical.

Is this a bug or a misuse of federation?

Sample to reproduce:

https://github.com/abc-moviestarplanet/GatewayResolverIssue/tree/main

[mcollina]

Thanks for reporting!

Can you provide steps to reproduce? We often need a reproducible example, e.g. some code that allows someone else to recreate your problem by just copying and pasting it. If it involves more than a couple of different file, create a new repository on GitHub and add a link to that.

[abc-moviestarplanet]

Here is a repository with steps to reproduce: https://github.com/abc-moviestarplanet/GatewayResolverIssue/tree/main

[mcollina]

@marco-ippolito could you take a look?

[marco-ippolito]

probably related to https://github.com/mercurius-js/mercurius-gateway/issues/22

[Drilmo]

Hi, have you find why it doesn't work ? i think my issue is the same 😭 https://github.com/mercurius-js/mercurius-gateway/issues/114 It's blocker for me....