To create getter, Add DatabaseEmbedding protocol to your state-tree.

struct RootState: DatabaseEmbedding {

  static let getterToDatabase: (RootState) -> RootState.Database = { $0.db }

  struct Database: DatabaseType {

  var db = Database()

Create getter from entity id

let id = Book.EntityID.init("some")

let derived: Book.Derived = storage.derived(from: id)

Get entity from Getter

let entity: Book = getter.value.wrapped

VergeORM supports create MemoizeSelector from Storage or Store.