Given I have a property

Class All.AllBooks Extends %Library.Persistent
{

Property ID As %Integer;

Property Title As User.Book;

}

In the class method

ClassMethod GetABookById(id As %Integer) As %Status
{

SET MyBooks = ##class(All.Allbooks).%OpenId(id)

SET obj = {

     "ID" : (MyBooks.%Id())

     "Title" : (MyBooks.Title)

}

WRITE obj.%ToJSON()

Quit 1
}

How do Access the foreign key in JSON() data