type Review @key(fields: "id") {
  id: ID!
  body: String
  author: User @provides(fields: "username")
  product: Product
}

extend type User @key(fields: "id") {
  id: ID! @external
  username: String @external
  reviews: [Review]
}

extend type Product @key(fields: "upc") {
  upc: String! @external
  reviews: [Review]
}