ASP.NET Core MVC 验证失败

Question

I am new to ASP.NET Core MVC apps. I am trying to create a web app but I am having an issue about validating my model. I have added model code, controller code and razor page. My model validation fails because razor page doesn't start il model. normally I don't need iller model.

Would you mind anyone can help me about is there any easy solution about validation without custom validation. I am using .NET Core 6.0 and Visual Studio 2022

This is my model class

using System;
using System.Collections.Generic;

namespace OdevProject.Models
{
    public partial class Ilceler
    {
        public Ilceler()
        {
            Adreslers = new HashSet<Adresler>();
            Bolumlers = new HashSet<Bolumler>();
            Doktorlars = new HashSet<Doktorlar>();
            Hastanelers = new HashSet<Hastaneler>();
            Randevulars = new HashSet<Randevular>();
        }

        public int IlceId { get; set; }
        public int IlId { get; set; }
        public string IlceAd { get; set; } = null!;

        public virtual Iller Il { get; set; } = null!;
        public virtual ICollection<Adresler> Adreslers { get; set; }
        public virtual ICollection<Bolumler> Bolumlers { get; set; }
        public virtual ICollection<Doktorlar> Doktorlars { get; set; }
        public virtual ICollection<Hastaneler> Hastanelers { get; set; }
        public virtual ICollection<Randevular> Randevulars { get; set; }
    }
}

and this is controller

public async Task<IActionResult> Create([Bind("IlceId,IlId,IlceAd")] Ilceler ilceler)
{
    //var Il = new Iller { IlId = ilceler.Il.IlId, IlAd=ilceler.Il.IlAd };
    if (ModelState.IsValid)
    {
        var ilce = _context.Ilcelers.Where(x => x.IlceAd == ilceler.IlceAd).FirstOrDefault();

        if (ilce != null)
        {
            ViewBag.Message = "Exist";
            return View();
        }
        else
        {
            _context.Add(ilceler);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }
    }

    ViewData["IlId"] = new SelectList(await _context.Illers.ToListAsync(), "IlId", "IlAd");

    //ViewData["Illist"] = new SelectList(await _context.Illers.ToListAsync(), "IlId", "IlAd");
    //ViewData["IlId"] = new SelectList(_context.Illers, "IlId", "IlId", ilceler.IlId);
    return View(ilceler);
} 

and finally razor pages

@model OdevProject.Models.Ilceler 

@{
    ViewData["Title"] = "Create";
}

<h1>Create</h1>

<h4>Ilceler</h4>
<hr />
<div class="row">
    <div class="col-md-4">
        <form asp-action="Create">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">                
                <label asp-for="IlId" class="control-label"></label>                
               @* @Html.DropDownList("iller",(IEnumerable<SelectListItem>)ViewData["Illist"],"---Il Seciniz---");*@
                <select asp-for="IlId" class ="form-control" asp-items="ViewBag.IlId"></select>  
            </div>
            <div class="form-group">
                <label asp-for="IlceAd" class="control-label"></label>
                <input asp-for="IlceAd" class="form-control" /> 
                @if (ViewBag.Message != null && ViewBag.Message == "Exist")
        {
            <br /><span style="color:red;">Kayıt mevcut!!!</span>
        }
                <span asp-validation-for="IlceAd" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

<div> 
    <a asp-action="Index">Back to List</a>
</div>

@section Scripts {
    @{await Html.RenderPartialAsync("_ValidationScriptsPartial");}
}

Answer 1

As this document said:

Beginning with .NET 6, new projects include the <Nullable>enable</Nullable> element in the project file. Once the feature is turned on, existing reference variable declarations become non-nullable reference types .

So that the non-nullable property must be required in asp.net 6, otherwise the ModelState will be invalid.

You can remove <Nullable>enable</Nullable> from your project file.

Or you can choose to initialize the data like below:

public partial class Ilceler
{
    public Ilceler()
    {
        Il = new Iller();
        //...
    }
    public int IlceId { get; set; }
    public int IlId { get; set; }
    public string IlceAd { get; set; } = null!;

    public virtual Iller Il { get; set; }
    //...
}

Answer 2

First of all, thank you for your help. This is how I solved it. Is it the right approach? Or is there a more accurate method?

 public async Task<IActionResult> Create([Bind("IlceId,IlId,IlceAd")] Ilceler ilceler)
        {
            Iller Il = new Iller();
            Il = _context.Illers.Find(ilceler.IlId); 

            if (ModelState.IsValid)
            {
                var ilce = _context.Ilcelers.Where(x => x.IlceAd == ilceler.IlceAd).FirstOrDefault();
                if (ilce != null)
                {
                    ViewBag.Message = "Exist";
                    return View();
                }
                else
                {
                    _context.Add(ilceler);
                    await _context.SaveChangesAsync();
                    return RedirectToAction(nameof(Index));
                }
            }
            ViewData["IlId"] = new SelectList(await _context.Illers.ToListAsync(), "IlId", "IlAd");