如果在mvc4中找不到ID，则会显示错误消息

Question

My employee(Customer) diary is based on CustomerID, see this image .

If I am creating new Diary I need the CustomerID.

If I am using correct CustomerId that is present in database then it works properly, but if I am using an incorrect customerID then its showing the view to me and displaying error about other fields.

I just want to see the error message saying "ID not found"

Here is my create diary Code and image @nd image I just want to see an error message if I am putting in wrong customerID my Controller code for create Diary

// POST: /Diary/Create

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create(Diary diary)
    {
        if (ModelState.IsValid)
        {
            cd.Diaries.Add(diary);
            cd.SaveChanges();
            return RedirectToAction("Index","Home");
        }

        return PartialView("_CreateDiary");
    }

Answer 1

First add the condition to check based upon the entered CustomerId and add a model error if needed:

Controller

if (!cd.Customers.Any(c => c.Id == diary.CustomerId)
{
    ModelState.AddModelError("CustomerId", "Customer not found");
}

Then add the following to your view (or a ValidationSummary)

View

@Html.ValidationMessage("CustomerId")

I would advise displaying a list of customers that the user selects instead, this will improve the UI experience and also avoid errors like this.

Full controller code

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Diary diary)
{

   if (!cd.Customers.Any(c => c.Id == diary.CustomerId)
   {
    ModelState.AddModelError("CustomerId", "Customer not found");
    }
    if (ModelState.IsValid)
    {
        cd.Diaries.Add(diary);
        cd.SaveChanges();
        return RedirectToAction("Index","Home");
    }

    return PartialView("_CreateDiary");
}