Question

最近我再次拿起了我的EF 4.1 / MVC 3项目并开始构建实际的前端功能。

现在我正在开发一个“简单”的消息系统，但在转到该页面后，我收到标题中所述的错误

修改

它创建数据库而不是模型。

堆栈追踪：

[NullReferenceException：对象引用未设置为的实例   对象。] ASP._Page_Views_Inbox_Index_cshtml.Execute（）in   C：\开发\ MVC \ DOCCL \查看\收件箱\ Index.cshtml：18
  System.Web.WebPages.WebPageBase.ExecutePageHierarchy（）+197
  System.Web.Mvc.WebViewPage.ExecutePageHierarchy（）+81
  System.Web.WebPages.StartPage.RunPage（）+17
  System.Web.WebPages.StartPage.ExecutePageHierarchy（）+62
  System.Web.WebPages.WebPageBase.ExecutePageHierarchy（WebPageContext   pageContext，TextWriter writer，WebPageRenderingBase startPage）+76
  System.Web.Mvc.RazorView.RenderView（ViewContext viewContext，   TextWriter writer，Object instance）+222
  System.Web.Mvc.BuildManagerCompiledView.Render（ViewContext   viewContext，TextWriter writer）+115
  System.Web.Mvc.ViewResultBase.ExecuteResult（ControllerContext context）   +295 System.Web.Mvc.ControllerActionInvoker.InvokeActionResult（ControllerContext   controllerContext，ActionResult actionResult）+13
  System.Web.Mvc＆LT;＆GT; C_ DisplayClass1c.b _19（）   +23 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter（IResultFilter   filter，ResultExecutingContext preContext，Func 1 continuation) +242 System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>b__1b() +21 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList 1个过滤器，ActionResult actionResult）+177
  System.Web.Mvc.ControllerActionInvoker.InvokeAction（ControllerContext   controllerContext，String actionName）+324
  System.Web.Mvc.Controller.ExecuteCore（）+ 106   System.Web.Mvc.ControllerBase.Execute（RequestContext requestContext）   +91 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute（RequestContext   requestContext）+10
  System.Web.Mvc。＆lt;＆gt; c_ DisplayClassb.b _5（）+34
  System.Web.Mvc.Async。＆lt;＆gt; c_ DisplayClass1.b _0（）+19
  System.Web.Mvc.Async。＆lt;＆gt; c_ DisplayClass8 1.<BeginSynchronous>b__7(IAsyncResult _) +10 System.Web.Mvc.Async.WrappedAsyncResult 1.End（）+62 System.Web.Mvc。＆lt;＆gt; c _DisplayClasse.b_ d（）+48
  System.Web.Mvc.SecurityUtil.b _0（动作f）+7   System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust（Action action）   +22 System.Web.Mvc.MvcHandler.EndProcessRequest（IAsyncResult asyncResult）+60
  System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest（IAsyncResult的   结果）+9
  System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute（）   +9478661 System.Web.HttpApplication.ExecuteStep（IExecutionStep step，Boolean＆amp; completedSynchronously）+178

InnerException： {“列ID在规范中出现过多次。”}

最近添加的代码是。

控制器：

//
// GET: /Inbox/Index/5/1
public ActionResult Index(int? Id, int Page = 1)
{
    try
    {
        const int pageSize = 10;
        var messages = from m in horseTracker.Messages
                        where m.ReceiverId.Equals(Id)
                        select m;

        var paginatedMessages = new PaginatedList<Message>(messages, Page, pageSize);

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

    }
    return View();
}

模型

public class Message
{
    [Key]
    public int Id { get; set; }

    [Required(ErrorMessage = "Subject is required")]
    [Display(Name = "Subject")]
    public string Subject { get; set; }

    [Required(ErrorMessage = "Message is required")]
    [Display(Name = "Message")]
    public string Content { get; set; }

    [Required]
    [Display(Name = "Date")]
    public DateTime Created { get; set; }

    public Boolean Read { get; set; }

    [Required(ErrorMessage = "Can't create a message without a user")]
    public int SenderId { get; set; }
    public virtual User Sender { get; set; }

    [Required(ErrorMessage = "Please pick a recipient")]
    public int ReceiverId { get; set; }
    public virtual User Receiver { get; set; }
}

public class User
{
    [Key]
    public int Id { get; set; }

    [Required]
    [Display(Name = "Username")]
    public string UserName { get; set; }

    [Required]
    [Display(Name = "First Name")]
    public string FirstName { get; set; }

    [Required]
    [Display(Name = "Last Name")]
    public string LastName { get; set; }

    [Required]
    [Display(Name = "E-Mail")]
    public string Email { get; set; }

    [Required]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [Required]
    [Display(Name = "Country")]
    public string Country { get; set; }

    public string EMail { get; set; }

    //Races
    public virtual ICollection<Message> Messages { get; set; }
}

modelBuilder.Entity<User>()
    .HasMany(u => u.Messages)
    .WithRequired(m => m.Receiver)
    .HasForeignKey(m => m.ReceiverId)
    .WillCascadeOnDelete(false);

任何人都知道为什么我会收到这个错误？在我添加这些类之前，它工作正常。

Answer 1

在您的消息模型中，Id不可为空，但您的操作允许空值，EF无法在查询和放大器的where子句中匹配这两种类型。抛出一个例外。

列ID在规范中出现多次

1 个答案: