public BookAuthorModel GetBookAuthorById(int bookid, int authorid)
        {
            var book=this.bookFacade.GetBookById(bookid);
            var author = this.authorFacade.GetAuthorById(authorid);
            if (book == null)
            {
                return null;
            }

            if (author == null)
            {
                return null;
            }

            var bookauthor = new BookAuthorModel { BookName = book.Name, AuthorName = author.FirstName + " " + author.LastName, BookId = book.Id, AuthorId = author.Id };
            return bookauthor;
        }