ASP.NET提交表单时Enigma的Game属性无法填充求助

作为ASP.NET新手，在添加Enigma（谜题）时需要关联雷顿教授系列的对应游戏，为此制作了对应数据库游戏的下拉选择框，但提交表单时，Enigma的必填Game字段未被填充，导致验证失败。

视图代码 #

@model ProfessorLayton.Models.Enigma

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

<h2>Add an enigma to the current list of enigmas</h2>

<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="Name" class="control-label"></label>
                <input asp-for="Name" class="form-control" />
                <span asp-validation-for="Name" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Content" class="control-label"></label>
                <input asp-for="Content" class="form-control" />
                <span asp-validation-for="Content" class="text-danger"></span>
            </div>
            <br>
            Chose the game in which this enigma is in :
            <div class="form-group">
                <select asp-for="GameId" class="form-control" asp-items="ViewBag.GameId"></select>
                <span asp-validation-for="GameId" class="text-danger"></span>
            </div>
            <br>
            <div class="form-group">
                <input type="submit" value="Ajouter l'énigme" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

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

控制器代码 #

//GET: enigma/Create
public async Task<IActionResult> Create()
{
    var enigma = await _context.Enigmas
        .Include(g=>g.Game)
        .Include(s=>s.Solution)
        .ToListAsync();
    var availableGamesQuery=from g in _context.Games select g;
    var availableGames=availableGamesQuery.ToList();
    ViewData["Enigma"]=enigma;  
    ViewData["GameId"]=new SelectList(availableGames,"Id","Title")  ;                      
    return View();
}

//Méthode d'action pour l'ajout d'une enigme
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("Id,Name,Content,GameId")] Enigma enigma,List<Game> games)
{
    // Apply model validation rules
    if (ModelState.IsValid)
    {
        _context.Add(enigma);
        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }
    else
    {
    // At this point, something failed: redisplay form
    // var allErrors = ModelState.Values.SelectMany(v => v.Errors.Select(b => b.ErrorMessage));
    // return Json(new {allErrors});
    return View(enigma);
    }
}

核心问题 #

1. POST方法验证失败返回视图时，未重新填充ViewBag.GameId的下拉选项，导致下拉框为空，用户无法重新选择游戏，进而触发Game字段必填验证错误
2. POST方法参数中的List<Game> games无实际作用，属于冗余参数
3. 视图顶部未使用的Game game = (Game)ViewData["Game"]!;可能引发空引用异常

修复步骤 #

1. 修复POST方法，重新填充下拉选项 #

当ModelState验证失败时，必须重新加载游戏列表并赋值给ViewBag.GameId，确保回传页面后下拉框有选项可选择：

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("Id,Name,Content,GameId")] Enigma enigma)
{
    if (ModelState.IsValid)
    {
        _context.Add(enigma);
        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }
    // 验证失败时重新填充下拉选项
    var availableGames = await _context.Games.ToListAsync();
    ViewData["GameId"] = new SelectList(availableGames, "Id", "Title");
    return View(enigma);
}

2. 移除冗余代码 #

• 删除POST方法参数中的List<Game> games
• 删除视图顶部的Game game = (Game)ViewData["Game"]!;

3. 优化GET方法（可选） #

GET方法中获取所有Enigma的代码无意义，可简化：

//GET: enigma/Create
public async Task<IActionResult> Create()
{
    var availableGames = await _context.Games.ToListAsync();
    ViewData["GameId"] = new SelectList(availableGames, "Id", "Title");                    
    return View();
}

4. 确保模型验证配置正确 #

确认Enigma模型中GameId字段标记了必填验证：

public class Enigma
{
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    [Required]
    public string Content { get; set; }
    [Required(ErrorMessage = "请选择游戏")]
    public int GameId { get; set; }
    public Game Game { get; set; }
    // 其他属性...
}

内容的提问来源于stack exchange，提问作者Klaph