# federation v1 definition
directive @external on FIELD_DEFINITION

# federation v2 definition
directive @external on OBJECT | FIELD_DEFINITION

The @external directive is used to mark a field as owned by another service. This allows service A to use fields from service B while also knowing at runtime the types of that field. @external directive is only applicable on federated extended types. All the external fields should either be referenced from the @key, @requires or @provides directives field sets.

Due to the smart merging of entity types, @external directive is no longer required on @key fields and can be omitted from the schema. @external directive is only required on fields referenced by the @requires and @provides directive.

Example: Given

@KeyDirective(FieldSet("id"))
@ExtendsDirective
class Product(@ExternalDirective val id: String) {
  fun newFunctionality(): String = "whatever"
}

should generate

type Product @extends @key(fields : "id") {
  id: String! @external
  newFunctionality: String!
}