/// <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);
}
