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

# Orders service
extend type User @key(fields: "id") {
  id: ID! @external
  orders: [Order!]!
}

// ❌ N+1 queries
User: { orders: (u) => db.orders.findByUserId(u.id) }

// ✅ DataLoader batch
const loader = new DataLoader(async (ids) => {
  const orders = await db.orders.findByUserIds(ids);
  return ids.map(id => orders.filter(o => o.userId === id));
});
User: { orders: (u) => loader.load(u.id) }

type UserConnection {
  edges: [{ node: User!, cursor: String! }]!
  pageInfo: { hasNextPage: Boolean!, endCursor: String }!
}

type CreateUserPayload {
  user: User
  errors: [{ field: String, message: String! }]
}