ASP.NET Core MVC model validation in viewmodel with base model

Question

I am developing a web app with ASP.NET Core MVC, and I have a problem with model validation.

When I set validation in class and then use it in view model, validation does not work. How can I struggle with it?

This is my code:

public class Il : IEntity
{
    [Required(ErrorMessage = "Kodu boş geçilemez")]
    public int IlKodu { get; set; }
    public int UlkeId { get; set; }
    [Required(ErrorMessage = "Ad boş geçilemez")]
    public string Ad { get; set; }
    public int Id { get; set; }
    public DateTime? KayitTarihi { get; set; }
    public DateTime? GuncellemeTarihi { get; set; }
}

ViewModel class;

public class IlAddViewModel
{
    public Il Il { get; set; }
    public List<Ulke> Ulkeler{ get; set; }
}

Then the view:

<div class="container pt-4 eklemeDiv col-4">
<form  asp-controller="Il" asp-action="Add" asp-area="Admin" method="post">
    <div class="form-group">
        <label asp-for="Il.IlKodu">Il Kodu</label>
        <input asp-for="Il.IlKodu" class="form-control" placeholder="İl Kodu Giriniz">
        <span asp-validation-for="Il.IlKodu" class="text-danger"></span>
    </div>

    <div class="form-group">
        <label asp-for="Il.Ad">Il Kodu</label>
        <input asp-for="Il.Ad" class="form-control" placeholder="İl Kodu Giriniz">
        <span asp-validation-for="Il.Ad" class="text-danger"></span>
    </div>

    <div class="form-group">
        <label >Ülke</label>
        <select style="width: 100%;height:30px" id="selectIl" asp-for="Il.UlkeId"
                asp-items="@(new SelectList(Model.Ulkeler,"Id","Ad"))">
            <option>Lütfen Seçim Yapınız</option>
        </select>
    </div>


    <input id="btnIlEkle" type="submit" value="Ekle" class="btn btn-xs btn-success" />
    <a class="btn btn-xs btn-primary" asp-action="Anasayfa" asp-area="Admin" asp-controller="Admin"><i class="fas fa-chevron-left"></i>Anasayfaya Dön</a>
</form>
</div>

The view model does not show validation messages in view. And also how can I show validation messages for list elements?

Answer 1

My friends, all parts of my code are correct for structure, just one error is missing and finally i found it today. I am sharing this solution to help others;

Also controller code;

[HttpPost]
    public async Task<ActionResult> Add(IlAddViewModel ilAddViewModel)
    {
        
        var kayitVarmi = _ilService.BenzerKayitVarMi(ilAddViewModel.Il.IlKodu, ilAddViewModel.Il.Ad);
        if (kayitVarmi)
        {
            TempData.Add("Hata", "Böyle bir kayıt mevcut");
            return RedirectToAction("Add");
        }
        else
        {
            if (ModelState.IsValid && !kayitVarmi)
            {
                ilAddViewModel.Il.KayitTarihi = DateTime.Now;
                await _ilService.Add(ilAddViewModel.Il);                   
                TempData.Add("Message", String.Format("{0} başarıyla eklendi", ilAddViewModel.Il.Ad));
                return RedirectToAction("Anasayfa", "Admin", new { Area = "Admin" });

            }
        }
        return RedirectToAction("Add");
    }

To achieve this validation error, you must add necessary javascript packages as below;

<script src="~.../jquery-validation/dist/jquery.validate.js"></script>
<script src="~.../jquery-validation-unobtrusive/dist/jquery.validate.unobtrusive.js"></script>

These javascript packages help to show validation messages without making post to action method.

Answer 2

In the controller you will have access to check the model state to verify if it is valid or not. The controller code should like this

public class HomeController : Controller  
{  
    // GET: Home  
    public ActionResult Index()  
    {  
        return View();  
    }  

    [HttpGet]  
    public ActionResult Create()  
    {  
        return View();  
    }  

    [HttpPost]  
    public ActionResult Create(Employee employee)  
    {  
        try  
        {  
//Here ModelState.IsValid will be true in case all the required fields that are mentioned in employee class
            if (ModelState.IsValid)  
            {  
               return RedirectToAction("Index");  
            }  

            return View();  
        }  
        catch (Exception)  
        {  
            return View();  
        }  
    }  
}