兒童班級不能使用的枚舉列表

Question

我正在創建一個幫助臺軟件的網頁，其中頂部顯示票務類中的信息，然後顯示通過ICollection附加到票證類的票證底部。目前，如果我註釋掉底部，則頂部（靜態表）可以正常工作。但是，指向ICollection的底部兩個表格不起作用。下面是我得到的錯誤：

這是我的觀點：

@model HelpDesk.Model.Ticket 

@{ 
    ViewBag.Title = "Ticket# " + Html.DisplayFor(model => model.TicketNumber); 
} 

<table class="table"> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.CategoryId) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.Category.CategoryName) 
     </th> 
    </tr> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.OpenUserId) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.OpenUser.FullName) 
     </th> 
    </tr> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.OpenDate) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.OpenDate) 
     </th> 
    </tr> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.TechnicianId) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.Technician.FullName) 
     </th> 
    </tr> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.TicketStatusId) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.TicketStatus.StatusDescription) 
     </th> 
    </tr> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.CloseDate) 
     </th> 
     <th> 
      @Html.DisplayFor(model => model.CloseDate) 
     </th> 
    </tr> 
    <tr></tr> 
</table> 

<table class="table"> 
    <tr> 
     <th> 
      @Html.DisplayNameFor(model => model.TicketNotes.Note) 
     </th> 
     <th> 
      @Html.DisplayNameFor(model => model.TicketNotes.TicketNoteDate) 
     </th> 
     <th> 
      @Html.DisplayNameFor(model => model.TicketNotes.UserNote.FullName) 
     </th> 
     <th></th> 
    </tr> 

    @foreach (var item in Model.TicketNotes) 
    { 
     <tr> 
      <td> 
       @Html.DisplayFor(modelItem => item.TicketNotes.Note) 
      </td> 
      <td> 
       @Html.DisplayFor(modelItem => item.TicketNotes.TicketNoteDate) 
      </td> 
      <td> 
       @Html.DisplayFor(modelItem => item.TicketNotes.UserNote.FullName) 
      </td> 
     </tr> 
    } 

</table> 

這是我的控制器代碼：

public ActionResult EditUserTicket(Guid id) 
     { 
      Ticket ticket = tickets.GetById(id); 

      var model = db.Tickets 
        .Include(t => t.TicketNotes) 
        .Where(t => t.TicketId == id).First(); 

      return View(model); 
     } 

，這裏是我的模型：

namespace HelpDesk.Model 
{ 
    public class Ticket 
    { 
     public Ticket() 
     { 
      this.TicketNotes = new HashSet<TicketNote>(); 
     } 
     public Guid TicketId { get; set; } 

     [Display(Name = "#")] 
     [DatabaseGenerated(DatabaseGeneratedOption.Identity)] 
     [Required] 
     public int TicketNumber { get; set; } 

     [ForeignKey("Category")] 
     [Required] 
     public Guid CategoryId { get; set; } 

     public virtual Category Category { get; set; } 

     [ForeignKey("OpenUser")] 
     [Required] 
     public Guid OpenUserId { get; set; } 

     [Display(Name = "Ticket Owner")] 
     public virtual User OpenUser { get; set; } 

     [Display(Name = "Opened")] 
     [DataType(DataType.Date)] 
     [Required] 
     public DateTime OpenDate { get; set; } 

     [ForeignKey("Technician")] 
     [Required] 
     public Guid TechnicianId { get; set; } 

     [Display(Name = "Technician")] 
     public virtual User Technician { get; set; } 

     [ForeignKey("TicketStatus")] 
     [Required] 
     public Guid TicketStatusId { get; set; } 

     public virtual TicketStatus TicketStatus { get; set; } 

     [Display(Name = "Closed")] 
     [DataType(DataType.Date)] 
     public Nullable<DateTime> CloseDate { get; set; } 

     [Display(Name = "Note")] 
     public virtual ICollection<TicketNote> TicketNotes { get; set; } 
     //public virtual ICollection<TicketSubscription> TicketSubscriptions { get; set; } 
    } 
}