Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// users-subgraph/schema.graphql
extend schema @link(url: "https://specs.apollo.dev/federation/v2.0", import: ["@key"])

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

type Query {
  user(id: ID!): User
  me: User
}

// orders-subgraph/schema.graphql — extends User from users-subgraph
extend schema @link(url: "https://specs.apollo.dev/federation/v2.0", import: ["@key", "@external"])

type User @key(fields: "id") {
  id: ID! @external        # owned by users-subgraph
  orders: [Order!]!        # added by this subgraph
}

type Order {
  id: ID!
  total: Float!
  status: String!
}

type Query {
  order(id: ID!): Order
}

// orders-subgraph/resolvers.js
const resolvers = {
  User: {
    // Federation calls this to load user's orders
    orders: (user) => db.orders.findAll({ userId: user.id }),
    // Reference resolver: reconstitute User from { id }
    __resolveReference: (ref) => ({ id: ref.id }),
  },
};

// Apollo Router config (router.yaml):
// supergraph:
//   listen: 0.0.0.0:4000
// subgraphs:
//   users:  { routing_url: http://users-service:4001/graphql }
//   orders: { routing_url: http://orders-service:4002/graphql }