public IHttpActionResult GetBook(int id)
        {
            var book = context.Books.Find(id);
            if (book == null)
            {
                return NotFound();
            }

            var bookViewModel = new BookViewModel(book);

            return this.Ok(bookViewModel);
        }
        public IHttpActionResult DeleteBook(int id)
        {
            Book book = context.Books.Find(id);
            if (book == null)
            {
                return NotFound();
            }

            context.Books.Remove(book);
            context.SaveChanges();

            var bookViewModel = new BookViewModel(book);

            return Ok(bookViewModel);
        }