internal void PrepareForCreateNew()
 {
     foreach (var a in _unitOfWork.Repo.GetAuthors())
     {
         AuthorSelectList.Add(new SelectListItem
         {
             Text  = a.FullName,
             Value = a.AuthorId.ToString(),
         });
     }
 }
        /// <summary>
        /// Fills AuthorSelectList and AuthorName string property
        /// </summary>
        /// <param name="id">Id from BOOOK MODEL!!!!</param>
        internal void PreparForEdit(int id)
        {
            var book = _unitOfWork.Repo.GetBooks().FirstOrDefault(b => b.BookId == id);

            //micanje starog autora
            var oldAuthor = _unitOfWork.Repo.GetAuthors().FirstOrDefault(b => b.AuthorId == book.AuthorId);

            oldAuthor.Books.Remove(book);

            foreach (var a in _unitOfWork.Repo.GetAuthors())
            {
                AuthorSelectList.Add(new SelectListItem
                {
                    Text  = a.FullName,
                    Value = a.AuthorId.ToString(),
                });
            }
        }