Global IDs

Viaduct uses two different Kotlin types to represent GraphQL ID types: GlobalID<T> and String. GlobalID is an object that consists of a type and an internal ID. They are used to uniquely identify node objects in the graph. GlobalID values support structural equality, as opposed to referential equality.

There are two conditions under which GlobalID<T> will be used:

1. The id field of a Node object type
2. A field of type ID with the @idOf(type:"T") directive, where T must be a GraphQL object or interface type that implements Node

Elsewhere in the Kotlin code, String will be used for IDs.

For the examples below, id, id3 and f2 are GlobalIDs and while id2 and f1 are Strings.

type MyNode implements Node {
  id: ID!
  id2: ID!
  id3: ID! @idOf(type: "MyNode")
}

input Input {
  f1: ID!
  f2: ID! @idOf(type: "MyNode")
}

If a Node object type implements an interface, and that interface has an id field, then that interface must also implement Node.

Instances of GlobalID can be created using the Context objects provided to resolvers, e.g., ctx.globalIDFor(User.Reflection, "123").