What is it

GraphQL has a built-in ID scalar type, which represents a unique identifier.

• often used to refetch an object or as the key for a cache.

The ID type is serialized in the same way as a String

• however, defining it as an ID signifies that it is not intended to be human‐readable.

It is best to rely on existing libs or tool sets that provide handling of object identifiers

You can specify a unique identifier for any object you query.

• Apollo Client assumes that all objects with the same object identifier represent the same piece of information.

Even if the entrypoint or the query looks different, GraphQL recognizes the queries as the same object and caches/returns it:

query {
  author(name: "Arthur Goldhammer") {
    coauthors {
      name
      id
    }
  } 
}

query {
  author(id: "5") {
    name
    id
  }
}