提交表单时所有输入字段被清除 ASP.NET

Question

I'm creating a simple MVC project for my ASP.NET classes at the Uni. It consists of one model class (BikeAds), Controller (BikeAdsController) and Views (Create, Delete, Details, Edit, Index) and uses mdf file as a database.

Controller and views were generated automatically (I chose "MVC controller with views, using Entity Framework").

I encountered the problem when trying to create a new entry. When I fill the "Create" form and click "Submit" button, it clears all data from the input fields and the form is not submitted - validation doesn't allow for empty fields. When I removed [Required] validation, I got a SQL exception (null is not allowed in the database).

I do not understand where the cause of the issue my lie.

Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.EntityFrameworkCore;
using bikes_ads.Data;
using bikes_ads.Models;

namespace bikes_ads.Controllers
{
    public class BikeAdsController : Controller
    {
        private readonly BikesAdvertsDbContext _context;

        public BikeAdsController(BikesAdvertsDbContext context)
        {
            _context = context;
        }

        // GET: BikeAds
        public async Task<IActionResult> Index()
        {
            return View(await _context.Adverts.ToListAsync());
        }

        // GET: BikeAds/Details/5
        public async Task<IActionResult> Details(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var bikeAd = await _context.Adverts
                .FirstOrDefaultAsync(m => m.Id == id);
            if (bikeAd == null)
            {
                return NotFound();
            }

            return View(bikeAd);
        }

        // GET: BikeAds/Create
        public IActionResult Create()
        {
            return View();
        }

        **// POST: BikeAds/Create
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Create([Bind("Id")] BikeAd bikeAd)
        {
            if (ModelState.IsValid)
            {
                _context.Add(bikeAd);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            return View(bikeAd);
        }**

        // GET: BikeAds/Edit/5
        public async Task<IActionResult> Edit(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var bikeAd = await _context.Adverts.FindAsync(id);
            if (bikeAd == null)
            {
                return NotFound();
            }
            return View(bikeAd);
        }

        // POST: BikeAds/Edit/5
        // To protect from overposting attacks, enable the specific properties you want to bind to, for 
        // more details, see http://go.microsoft.com/fwlink/?LinkId=317598.
        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(int id, [Bind("Id")] BikeAd bikeAd)
        {
            if (id != bikeAd.Id)
            {
                return NotFound();
            }

            if (ModelState.IsValid)
            {
                try
                {
                    _context.Update(bikeAd);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!BikeAdExists(bikeAd.Id))
                    {
                        return NotFound();
                    }
                    else
                    {
                        throw;
                    }
                }
                return RedirectToAction(nameof(Index));
            }
            return View(bikeAd);
        }

        // GET: BikeAds/Delete/5
        public async Task<IActionResult> Delete(int? id)
        {
            if (id == null)
            {
                return NotFound();
            }

            var bikeAd = await _context.Adverts
                .FirstOrDefaultAsync(m => m.Id == id);
            if (bikeAd == null)
            {
                return NotFound();
            }

            return View(bikeAd);
        }

        // POST: BikeAds/Delete/5
        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> DeleteConfirmed(int id)
        {
            var bikeAd = await _context.Adverts.FindAsync(id);
            _context.Adverts.Remove(bikeAd);
            await _context.SaveChangesAsync();
            return RedirectToAction(nameof(Index));
        }

        private bool BikeAdExists(int id)
        {
            return _context.Adverts.Any(e => e.Id == id);
        }
    }
}

Create form:

@model bikes_ads.Models.BikeAd

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

<h1>Create</h1>

<h4>BikeAd</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="Title" class="control-label"></label>
                <input asp-for="Title" class="form-control" />
                <span asp-validation-for="Title" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Category" class="control-label"></label>
                <input asp-for="Category" class="form-control" />
                <span asp-validation-for="Category" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="ShortDescription" class="control-label"></label>
                <input asp-for="ShortDescription" class="form-control" />
                <span asp-validation-for="ShortDescription" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="LongDescription" class="control-label"></label>
                <input asp-for="LongDescription" class="form-control" />
                <span asp-validation-for="LongDescription" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="SellerName" class="control-label"></label>
                <input asp-for="SellerName" class="form-control" />
                <span asp-validation-for="SellerName" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="SellerPhoneNumber" class="control-label"></label>
                <input asp-for="SellerPhoneNumber" class="form-control" />
                <span asp-validation-for="SellerPhoneNumber" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Price" class="control-label"></label>
                <input asp-for="Price" class="form-control" />
                <span asp-validation-for="Price" 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");}
}

Model class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.ComponentModel.DataAnnotations;

namespace bikes_ads.Models
{
    public class BikeAd
    {
        [Key]
        public int Id { get; set; }
        [Required]
        [MaxLength(50)]
        public string Title { get; set; }
        [Required]
        public string Category { get; set; }
        [Required]
        [MaxLength(100)]
        public string ShortDescription { get; set; }
        [Required]
        [MaxLength(500)]
        public string LongDescription { get; set; }
        [Required]
        public string SellerName { get; set; }
        [Required]
        public string SellerPhoneNumber { get; set; }
        [Required]
        public double Price { get; set; }

        public BikeAd(int id, string title, string category, string shortDescription, string longDescription, string sellerName, string sellerPhoneNumber, double price)
        {
            Id = id;
            Title = title;
            Category = category;
            ShortDescription = shortDescription;
            LongDescription = longDescription;
            SellerName = sellerName;
            SellerPhoneNumber = sellerPhoneNumber;
            Price = price;
        }

        public BikeAd()
        {

        }

    }
}

Answer 1

In your HTTPPost Create method, you're only binding the Id property;

public async Task<IActionResult> Create([Bind("Id")] BikeAd bikeAd)
{
}

Looking at your create form, you have other properties besides Id .

1) Shouldn't you be binding the all the other properties?

and

2) Shouldn't Id be automatically generated?

Change your Create method to this;

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("Title,Category,Description,ShortDescription,LongDescription,SellerName,SellerPhoneNumber,Price")] BikeAd bikeAd)
{
   if (ModelState.IsValid)
   {
      _context.Add(bikeAd);
      await _context.SaveChangesAsync();
      return RedirectToAction(nameof(Index));
   }

   return View(bikeAd);
}