/// <summary> /// Default constructor assigning new <see cref="Guid"/> becuase entity live also un-persisted. /// </summary> public Book(Library library, string isbn) { AssertUtils.IsTrue(!string.IsNullOrEmpty(isbn)); AssertUtils.IsTrue(library != null, "Library is mandatory for book construction."); Id = Guid.NewGuid(); Isbn = isbn; Library = library; library.AddBook(this); }