public IActionResult NewFolder(NewFolderViewModel data) { if (data.ParentId == -1) { return(RedirectToAction("Index", new { errorId = "NewFolder", errorMsg = "Wybierz rodzica" })); } var error = treeService.AddNewFolder(data); if (error != null) { return(RedirectToAction("Index", new { errorId = "NewFolder", errorMsg = error })); } return(RedirectToAction("Index")); }