public int Create(DbBook book)
        {
            var newId = _books.Any() ? (_books.Max(x => x.Id) + 1) : 1;

            book.Id = newId;
            _books.Add(book);

            return(newId);
        }
        public void Update(DbBook book)
        {
            var dbbook = Get(book.Id);

            dbbook.ISBN        = book.ISBN;
            dbbook.Pages       = book.Pages;
            dbbook.Title       = book.Title;
            dbbook.Publisher   = book.Publisher;
            dbbook.PublishDate = book.PublishDate;
        }