public string Save(Book abook)
{
if (bookGateway.IsISBNExists(abook.Isbn))
{
return("ISBN exists");
}
if (abook.Isbn.Length != 13)
{
return("ISBN must thirteen 13 characters long.");
}
int rowAffected = bookGateway.Save(abook);
if (rowAffected > 0)
{
return("Book saved succesfully");
}
return("Book saved failed");
}