// Delete book
 public string DeleteBook(string bookId)
 {
     if (!String.IsNullOrEmpty(bookId))
     {
         try
         {
             int _bookId = Int32.Parse(bookId);
             using (LibroDBContext contextObj = new LibroDBContext())
             {
                 var _book = contextObj.libro.Find(_bookId);
                 contextObj.libro.Remove(_book);
                 contextObj.SaveChanges();
                 return("Libro eliminado correctamente");
             }
         }
         catch (Exception)
         {
             return("Error: libro no es valido");
         }
     }
     else
     {
         return("operacion no valido");
     }
 }
 // GET: All books
 public JsonResult GetAllBooks()
 {
     using (LibroDBContext contextObj = new LibroDBContext())
     {
         var bookList = contextObj.libro.ToList();
         return(Json(bookList, JsonRequestBehavior.AllowGet));
     }
 }
 //GET: Book by Id
 public JsonResult GetBookById(string id)
 {
     using (LibroDBContext contextObj = new LibroDBContext())
     {
         var bookId      = Convert.ToInt32(id);
         var getBookById = contextObj.libro.Find(bookId);
         return(Json(getBookById, JsonRequestBehavior.AllowGet));
     }
 }
 //Update Book
 public string UpdateBook(Libro book)
 {
     if (book != null)
     {
         using (LibroDBContext contextObj = new LibroDBContext())
         {
             int   bookId = Convert.ToInt32(book.Id);
             Libro _book  = contextObj.libro.Where(b => b.Id == bookId).FirstOrDefault();
             _book.Title     = book.Title;
             _book.Author    = book.Author;
             _book.Publisher = book.Publisher;
             _book.Isbn      = book.Isbn;
             contextObj.SaveChanges();
             return("Libro Actualizado correctamente");
         }
     }
     else
     {
         return("Error: libro no es valido");
     }
 }
 // Add book
 public string AddBook(Libro book)
 {
     try
     {
         if (book != null)
         {
             using (LibroDBContext contextObj = new LibroDBContext())
             {
                 contextObj.libro.Add(book);
                 contextObj.SaveChanges();
                 return("Libro registrado correctamente");
             }
         }
         else
         {
             return("Error: libro no es valido");
         }
     }
     catch (Exception ex)
     {
         throw ex;
     }
 }