Utility class that implements the basic
NestedSetDelegate interface.
Use this class if you already have an adjacency list model (parent/children
relationship mapped with a regular many-to-one property and a one-to-many collection) based
on a foreign key.
Interface implemented by domain model classes that represent a node in a nested set.
Usually used as a delegate, that is, an existing class that already has a parent/children
adjacency list adds a @OneToOne association to a delegate that implements this
interface.