Foreach 语句不能对 [Tracker.Models.INV_Assets] 类型的变量进行操作？

Question

我正在整理一个相当简单的 Code-First MVC5 库存跟踪应用程序。我已将我的应用程序添加到 Seed() 和我的所有维护表（位置、供应商、状态等），我可以查看/创建/编辑/删除。我现在正在为我的主要 [INV_Assets] 模型处理 View，但是当尝试通过我的模型中的项目 foreach 在表格中显示所有 [INV_Assets] 时，我收到错误：foreach statement cannot operate on variables of type 'Tracker.Models.INV_Assets' because 'Tracker.Models.INV_Assets' does not contain a public definition for 'GetEnumerator'。

下面是我[INV_Assets]的模型：

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using GridMvc.DataAnnotations;
using System.Web.Mvc;
using Tracker.Models;

namespace Tracker.Models
{
    [GridTable(PagingEnabled = true, PageSize = 30)]
    public class INV_Assets 
    {
        // Setting GridColumn Annotations allows you to use AutoGenerateColumns on view to auto create the Grid based on the model.


        public int Id { get; set; }

        public int Model_Id { get; set; }
        [ForeignKey("Model_Id")]
        public virtual INV_Models Model { get; set; }

        [Required]
        public int Manufacturer_Id { get; set; }
        [ForeignKey("Manufacturer_Id")]
        public virtual INV_Manufacturers Manufacturer { get; set; }

        [Required]
        public int Type_Id { get; set; }
        [ForeignKey("Type_Id")]
        public virtual INV_Types Type { get; set; }

        [Required]
        public int Location_Id { get; set; }
        [ForeignKey("Location_Id")]
        public virtual INV_Locations Location { get; set; }

        public int Vendor_Id { get; set; }
        [ForeignKey("Vendor_Id")]
        public virtual INV_Vendors Vendor { get; set; }

        [Required]
        public int Status_Id { get; set; }
        [ForeignKey("Status_Id")]
        public virtual INV_Statuses Status { get; set; }

        public string ip_address { get; set; }

        public string mac_address { get; set; }

        public string note { get; set; }
        public string owner { get; set; }
        public decimal cost { get; set; }
        public string po_number { get; set; }
        public string description { get; set; }

        public int invoice_number{ get; set; }

        [Required]
        public string serial_number { get; set; }

        [Required]
        public string asset_tag_number { get; set; }

        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime? acquired_date { get; set; }

        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime? disposed_date { get; set; }

        [Required]
        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime created_date { get; set; }

        [Required]
        public string created_by { get; set; }

        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime modified_date { get; set; }

        public string modified_by { get; set; }

        // Flag to specify if item is available? (Not signed out, not auctioned, recycled, etc.)
        //public bool available { get; set; }
    }
}

[INV_Assets] 视图：

@using GridMvc.Html
@model  Tracker.Models.INV_Assets

@{
    ViewBag.Title = "Home Page";
}
<table style="width:100%;">

@foreach (var item in Model) {
    <tr>
        <td>@Html.DisplayFor(modelItem => item.Status)</td>
        <td>@Html.DisplayFor(modelItem => item.Location)</td>
        <td>@Html.DisplayFor(modelItem => item.owner)</td>
        <td>@Html.DisplayFor(modelItem => item.Type)</td>
        <td>@Html.DisplayFor(modelItem => item.Manufacturer)</td>
        <td>@Html.DisplayFor(modelItem => item.Model)</td>
        <td>@Html.DisplayFor(modelItem => item.Vendor)</td>
        <td>@Html.DisplayFor(modelItem => item.description)</td>
        <td>@Html.DisplayFor(modelItem => item.asset_tag_number)</td>
        <td>@Html.DisplayFor(modelItem => item.serial_number)</td>
        <td>@Html.DisplayFor(modelItem => item.ip_address)</td>
        <td>@Html.DisplayFor(modelItem => item.mac_address)</td>
        <td>@Html.DisplayFor(modelItem => item.po_number)</td>
        <td>@Html.DisplayFor(modelItem => item.invoice_number)</td>
        <td>@Html.DisplayFor(modelItem => item.cost)</td>
        <td>@Html.DisplayFor(modelItem => item.note)</td>
        <td>@Html.DisplayFor(modelItem => item.acquired_date)</td>
        <td>@Html.DisplayFor(modelItem => item.disposed_date)</td>
        <td>@Html.DisplayFor(modelItem => item.created_date)</td>
        <td>@Html.DisplayFor(modelItem => item.created_by)</td>
        <td>@Html.DisplayFor(modelItem => item.modified_date)</td>
        <td>@Html.DisplayFor(modelItem => item.modified_by)</td>
    </tr>
}

</table>

我不太确定如何解决这个错误，并想知道是否有更多经验的人可以称重？

我的[INV_Locations] 模型/视图在做同样的事情时没有收到任何问题（不知道为什么）：

[INV_Locations]：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace Tracker.Models
{
    public class INV_Locations
    {
        public int Id { get; set; }
        public string location_dept { get; set; }
        public string location_room { get; set; }

        [Required]
        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime created_date { get; set; }

        [Required]
        public string created_by { get; set; }

        [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
        public DateTime modified_date { get; set; }

        public string modified_by { get; set; }
    }
}

[INV_Locations] 视图：

@model IEnumerable<Tracker.Models.INV_Locations>

@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h3>Maintenance - Locations</h3>

<p>
    @Html.ActionLink("Create New", "Create")
</p>
<table class="table">
    <tr>
        <th></th>
        <th>
            @*@Html.DisplayNameFor(model => model.location_dept)*@
            Dept:
        </th>
        <th>
            Room:
        </th>
        <th>
            Created:
        </th>
        <th>
            By:
        </th>
        <th>
            Modified:
        </th>
        <th>
            By:
        </th>
    </tr>

@foreach (var item in Model) {
    <tr>
        <td>
            @Html.ActionLink("Edit", "Edit", new { id = item.Id }) |
            @Html.ActionLink("Details", "Details", new { id = item.Id }) |
            @Html.ActionLink("Delete", "Delete", new { id = item.Id })
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.location_dept)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.location_room)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.created_date)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.created_by)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.modified_date)
        </td>
        <td>
            @Html.DisplayFor(modelItem => item.modified_by)
        </td>
    </tr>
}

</table>

我尝试在我的 [INV_Assets] View 上将 @model Tracker.Models.INV_Assets 更改为 @model IEnumerable<Tracker.Models.INV_Assets>（就像我的 [INV_Locations] View 拥有它一样。这允许我的解决方案构建，但是当尝试运行我的应用程序时View 我收到： System.InvalidOperationException The model item passed into the dictionary is of type 'Tracker.Models.INV_Assets', but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable 1[Tracker.Models.INV_Assets]'.

---

编辑 - 关于 Shyju 的建议：

我将我的HomeController Index() 更改为：

    TrackerContext _db = new TrackerContext();
    public ActionResult Index(INV_Assets defModel)
    {
        return View(defModel);
    }

到：

    TrackerContext _db = new TrackerContext();
    public ActionResult Index(INV_Assets defModel)
    {
        var assetList = new List<Tracker.Models.INV_Assets>();

        assetList.Add(defModel);
        return View(assetList);
    }

当我的视图现在加载时，我得到的只是表格 HTML：

<table style="width:100%;">

    <tr>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td>0</td>
        <td>0.00</td>
        <td></td>
        <td></td>
        <td></td>
        <td>01/01/0001</td>
        <td></td>
        <td>01/01/0001</td>
        <td></td>
    </tr>

</table>

我已确认我的 DBContext 中有 2 条完整的 [INV_Assets] 记录，但它们没有显示在视图中？如何将我的 [INV_Assets] 模型的所有实例正确加载到新的 assetList 变量中？

---

EDIT2：

将我的Index() 修改为：

    TrackerContext _db = new TrackerContext();
    public ActionResult Index(INV_Assets defModel)
    {
        var assetList = _db.INV_Assets.ToList(); // EXCEPTION
        return View(assetList);
    }

但是现在，在构建解决方案时，当我尝试运行应用程序时它会失败。详情如下：

错误：An exception of type 'System.Data.DataException' occurred in EntityFramework.dll but was not handled in user code. Additional information: An exception occurred while initializing the database. See the InnerException for details.

留言：An exception occurred while initializing the database. See the InnerException for details.

InnerException：{"The underlying provider failed on Open."}

来源：EntityFramework

Answer 1

您的视图绑定到Tracker.Models.INV_Assets 的单个实例。但是在您的视图中，您正试图循环遍历它。您需要确保传递给您的视图的是一个集合，以便我们可以循环遍历它。

在 INV 资产视图中，更改

@model Tracker.Models.INV_Assets

到

@model  List<Tracker.Models.INV_Assets>

您还需要确保从您的操作方法传递INV_Assets 对象的集合。

public ActionResult INVAssets()
{
  var assetList=new List<Tracker.Models.INV_Assets>();

  // Ex : manually adding one record. replace with your actual code to load data
  // to do : Add item to the list now
  assetList.Add(new INV_Assets { Name ="Test"});

  return View(assetList);     
}

编辑： 根据问题中的编辑

您的Index 操作不应将INV_Assets 的对象作为参数。

TrackerContext _db = new TrackerContext();
public ActionResult Index()
{
    var assetList =_db.INV_Assets.ToList();     
    return View(assetList);
}

假设 INV_Assets 是您的 TrackerContext 类的属性。如果您的属性名称不同，请更改上述代码以反映这一点。

如果您要加载特定位置的资产，请更新​​您的 Index 操作方法以接受位置 ID 作为参数。

public ActionResult Index(int id)
{
    var assetList =_db.INV_Assets.Where(s=>s.Location_Id==id).ToList();     
    return View(assetList);
}

所以你访问这个页面的网址是这样的

http://yoursitename/YourControllerName/Index/5

5 是一个有效的位置 ID，其中包含一些与之关联的资产。