AIP-156

Singleton resources

APIs sometimes need to represent a resource where exactly one instance of the resource always exists within any given parent. A common use case for this is for a settings object.

Guidance

An API may define singleton resources. A singleton resource must always exist by virtue of the existence of its parent, with one and exactly one per parent.

rpc GetSettings(GetSettingsRequest) returns (Settings) {
  option (google.api.http) = {
    get: "/v1/{name=users/*/settings}"
  };
}

rpc UpdateSettings(UpdateSettingsRequest) returns (Settings) {
  option (google.api.http) = {
    patch: "/v1/{settings.name=users/*/settings}"
  };
}
  • Singleton resources must not have a user-provided or system-generated ID; their resource name includes the name of their parent followed by one static-segment.
    • Example: users/1234/settings
  • Singleton resources must not define the Create, List, or Delete standard methods. The singleton is implicitly created or deleted when its parent is created or deleted.
  • Singleton resource should define the Get and Update methods, and may define custom methods as appropriate.