Filtering on fields across multiple subgraphs

Server
,
1

Hello,
Currently I’m working on a POC to migrate some of our frontend api’s to GraphQL with federation.

In one of the use cases I have the following two subgraphs(simplified for the sake of abbreviation).

# Organisation subgraph
type Query {
    organisationById(organisationId: ID!): Organisation
}

type Person @key(fields: "id") {
    id: ID!
    firstName: String
		lastName: String
		dateOfBirth: LocalDate!
	  organisation: Organisation
}

type Organisation {
    id: ID!
    name: String!
    user: [Person]!


# Authorization subgraph
type Person @key(fields: "id"){
    id: ID!
    roles: [Role!]!
}

type Role {
    id: ID!
    rolNaam: String!
    users: [Persoon]
}

type Query {
    userByRole(typeNaam: String!): Persoon
}

The subgraphs don´t share the same datasource. In fact, the authorization subgraph is connected to a 3rd party authorization provider.

Question 1
Our system has over 100 Organisations, each with tens of users. I want to query all persons having a certain role(say: organisation-administrator) within a given Organisation. So I want to define a query in one subgraph an limit the results by filtering on a field in another subgraph.

I also tried the suggestions with a combination of @required and @external directives but couldn’t really figure out how.

Question 2
From what I understand about federation I doubt if this is possible. Both subgraphs add and resolve their own fields on the Person type. When I query persons with a certain role, the Authorization subgraph resolves all persons with this role for all organisations.

When technically possible, the organisation subgraph would only resolve persons belonging to 1 Organisation. This would make the response inconsistent, because both subgraphs resolve a different number of persons.

Am I correct?

I’m using Apollo Server as Gateway and Spring-GraphQL for the subgraphs.

2

Hey there @steffen ! Have you taken a look at this article? Aggregating Data Across Subgraphs. It seems like your use case is similar to what’s defined in the article. Hope it helps!