MVC 4 - 使用 Entity Framework 更新模型 - 传递 httpPost 参数的空异常

Question

我正在学习 MVC 并尝试创建一个简单的表单，允许用户更新模型的描述。

问题是我得到一个空异常

The parameters dictionary contains a null entry for parameter 'ThreatID' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult GetThreat(Int32)' in 'RiskAssesmentApplication.Controllers.ThreatsController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

表单的 Get 方法似乎按预期工作，但 id 没有传回 HttpPost 方法参数，我不知道如何传递它。我运行搜索并看到了一些关于使用 @hiddenfor 助手的信息，但它对我不起作用。

这是我的方法

 public ActionResult GetThreat(int ThreatID)
        {
            // ViewModel.Threat = repository.GetThreat(ThreatID);
            RiskAssessmentApplicationEntities _DBContext = new RiskAssessmentApplicationEntities();
            ThreatWithSecurityEventAndISOControlViewModel ViewModel = new ThreatWithSecurityEventAndISOControlViewModel();
            ViewModel.Threat = _DBContext.Threats.Single(x => x.ID == ThreatID);
            ViewModel.SecurityEvents = _DBContext
                                        .ThreatHasSecurityEvents
                                        .Include("ThreatHasSecurityEvent.SecurityEvent")
                                        .Where(x => x.ThreatID == ThreatID)
                                        .Select(x => x.SecurityEvent);

            return View(ViewModel);                                   
        }

[HttpGet]
public ViewResult EditThreat(int ThreatID)
{
    Threat Threat = repository.Threats.FirstOrDefault(x => x.ID == ThreatID);
    return View(Threat);
}

[HttpPost]
public ActionResult EditThreat(Threat Threat)
{
    if (ModelState.IsValid)
    {
        repository.SaveThreat(Threat);
        TempData["message"] = string.Format("{0} new description has been saved", Threat.Description);
        return RedirectToAction("GetThreat");
    }
    else
    {
        // something is incorrect!
        return View(Threat);
    }
}

这是我的看法

@model RiskAssesmentApplication.Threat
@using RiskAssesmentApplication;
@{
    ViewBag.Title = "EditThreat";
}
<div style="font-family: Calibri">
    <fieldset>
        <legend>Edit Threat Description</legend>
        @using (Html.BeginForm())
        {
            @Html.HiddenFor(model => model.ID);
            <div class="editor-label">
                @Html.LabelFor(model => @Model.Description, "Threat Description")
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => @Model.Description)
                @Html.ValidationMessageFor(model => @Model.Description )
            </div> 
            <p>
                <input type="submit" value="Save Changes" />
            </p>
        }
    </fieldset>
</div>

这是我的模特

public class ThreatWithSecurityEventAndISOControlViewModel
    {
        public Threat Threat { get; set; }
        public SecurityEvent SecurityEvent { get; set; }
        public IEnumerable<ISOControl> ISOControls { get; set; }
        public IEnumerable<SecurityEvent> SecurityEvents { get; set; }

我真的很难过所以任何帮助将不胜感激

Answer 1

如果没有看到您的其余代码，很难确定，但听起来您正在使用一个断开连接的实体。仅仅因为您使用的实体模型具有数据库中行的 ID，并不意味着它已连接到您的数据上下文。使用 post 中传回的模型来查找连接的版本。示例：

[HttpPost]
public void Whatever(Threat model)
{
    var connectedModel = context.Threats.FirstOrDefault(x => x.ID == model.ID);
    connectedModel.SomeProperty = model.SomeProperty; //or use AutoMapper
    context.SaveChanges();   
}

Answer 2

将您的 RedirectToAction 替换为：

return RedirectToAction("EditThreat", new { ThreatID = 99 });

Answer 3

您的 GetThreat() 方法需要参数 int ThreatID（不可为空），但在您的 EditThreat() 方法中，您在重定向时不传递值。变化

return RedirectToAction("GetThreat");

至

return RedirectToAction("GetThreat", new { ThreatID = Threat.ID });

MVC 4 - 使用 Entity Framework 更新模型 - 传递 httpPost 参数的空异常

MVC4 - Updating Model using Entity Framework - Null Exception passing httpPost paramater

c#

entity-framework

nullreferenceexception

asp.net-mvc-4