Referencing types of another service that implement an interface

[mmuth]

Version: @apollo/[email protected]
Reproduction: https://github.com/mmuth/apollo-federation-interface-referencing
Related to: #336

Hi there!
I am using Apollo Federation in order to make references to types of other Services. I have a Project Service that offers several Project Types (SoftwareDevelopmentProject, MarketingProject etc) that implement a Project interface. Then I have a Service for the Access rights, where I basically just try to reference the Projects from the project Service by their ID. Due to #336 my current approach is to try using the concrete types (not the interface) to make references to the other Service. Unfortunately I cannot get the Project Service / Gateway to finally resolve the references.

My schema in the Projects Service looks like this:

  type Query {
    projects: [Project]
  }

  interface Project {
    id: ID!
    niceName: String!
    status: String!
  }

  type SoftwareDevelopmentProject implements Project @key(fields: "id") {
    id: ID!
    niceName: String!
    status: String!
    requiredEffortHours: Int!
  }

  type MarketingProject implements Project @key(fields: "id") {
    id: ID!
    niceName: String!
    status: String!
    budget: Int!
  }

And the Rights service with the types using extend and @key looks like this:

 type Query {
    user: User
  }

  type User {
    id: String!
    name: String!
    accessibleProjects: [Project]
  }

  extend interface Project {
    id: ID! @external
  }

  extend type SoftwareDevelopmentProject implements Project @key(fields: "id") {
    id: ID! @external
  }

  extend type MarketingProject implements Project @key(fields: "id") {
    id: ID! @external
  }

I did an analysis and the Apollo Gateway seems to request the Access-Rights Service for all Project IDs and then performs a Request to the Project Service. This request looks like:

Query:
"query($representations:[_Any!]!){_entities(representations:$representations){...on Project{niceName}}}"


Variables:
{
  "representations": []
}

What I would expect is that the representations Array is filled with the IDs and typenames of the Projects.
Also I noticed the ...on Project in the request, which is the interface, not the implementing types (even though __resolveType was called previously in the access rights Service), however this is might be not a real problem as I think it could be handled by the Projects Service.

[ivaylo-andonov]

I have the same issue - need to reference interface or union from one service to another. Seems that it's not supported from Apollo Federation as per their docs : An entity's @key cannot include fields that hold unions or interfaces. link and sounds reasonable to me for union types, because they don't contain any fields where to put @key directive which consist primary key, but seems possible idea to be supported for interfaces. Thoughts ?

Also to resolve interface Project from the second service you need to provide __resolveReference and __resolveType in the typed Project resolver , no ?

[Luscha]

Same problem here.
I have an elastic search service that returns an array of Metadata Interfaces (id, type, ....) and a Dgraph service that holds the Metadata implementations.

Had to create an UNION type in the elasticsearch Apollo server using all the implementation of the Metadata.

I still can't figure out if it is my Apollo Federation's design to be wrong, or if it is Apollo Federation to be not production ready.