延遲加載相關實體不與實體框架5.0工作

Question

我使用實體框架5在我的項目中首先使用數據庫。我相信在外鍵虛擬字段中延遲加載值時存在一些問題，並且我嘗試了各種方法，但目前爲止我無法解決此問題。

下面是詳細信息：

我有一個CustomerDiscountCardController指數方法如下：

public ActionResult Index(String searchTerm = null, int page = 1) 
     { 
      var model = CustomerDiscountCardPagedList(searchTerm, page); 


      ViewBag.CustomerID = new SelectList(db.Customers.OrderBy(c => c.FirstName), "CustomerID", "FirstName"); 
      if (Request.IsAjaxRequest()) 
      { 
       return PartialView("_CustomerDiscountCard", model); 
      } 
      return View(model); 
     } 

     private IPagedList<CustomerDiscountCard> CustomerDiscountCardPagedList(String searchTerm, int page) 
     { 
      var model = db.CustomerDiscountCards.Include(d => d.DiscountCard). 
       OrderBy(c => c.DiscountCard.CardName). 
       Where(c => (c.DiscountCard.CardName.Contains(searchTerm))). 
       Select(c => new 
       { 
        DiscountCardID = c.DiscountCardID, 
        CustomerID = c.CustomerID, 
        IssueDate = c.IssueDate, 
        ExpiryDate = c.ExpiryDate, 
        CustomerDiscountCardID = c.CustomerDiscountCardID 
       } 
       ).ToList().Select(c => new CustomerDiscountCard 
       { 
        DiscountCardID = c.DiscountCardID, 
        CustomerID = c.CustomerID, 
        IssueDate = c.IssueDate, 
        ExpiryDate = c.ExpiryDate, 
        CustomerDiscountCardID = c.CustomerDiscountCardID 

       }).ToPagedList(page, 4); 
      return model; 
     } 

我的數據上下文類看起來如下：

public OnlineFoodOrderingEntities2() 
     : base("name=OnlineFoodOrderingEntities2") 
    { 
     this.Configuration.LazyLoadingEnabled = true; 
     this.Configuration.ProxyCreationEnabled = true; 
    } 
    //Entities class code.... 

} 

我的自動生成的CustomerDiscountCard類看起來如下所示：

public partial class CustomerDiscountCard 
{ 
    public int CustomerDiscountCardID { get; set; } 
    public Nullable<int> DiscountCardID { get; set; } 
    public Nullable<int> CustomerID { get; set; } 
    public Nullable<System.DateTime> IssueDate { get; set; } 
    public Nullable<System.DateTime> ExpiryDate { get; set; } 
    public virtual Customer Customer { get; set; } 
    public virtual DiscountCard DiscountCard { get; set; } 
} 

現在的問題是當我的索引方法被調用Ajax請求返回_CustomerDiscountCard

佈局的代碼的局部佈局是如下：

@using PagedList; 
@using PagedList.Mvc; 
@using OnlineFoodOrderingMVC.Models; 
@model IPagedList<CustomerDiscountCard> 

<div id="targetCustomerDiscountCardList"> 

    <div class="pagedList" data-ofo-target="#targetCustomerDiscountCardList"> 

     @Html.PagedListPager(Model, page => Url.Action("Index", "CustomerDiscountCard", new { page }), 
     PagedListRenderOptions.MinimalWithItemCountText) 
    </div> 
    <div style="clear:both"></div> 
    <div> 
     <table class="entity_record_table"> 
      <tr class="entity_record_table_header"> 
       <th class="entity_record_table_header_item_text"> 
        CustomerDiscountCards 
       </th> 
       <th class="entity_record_table_header_link_text"> 
        Edit 
       </th> 
       <th class="entity_record_table_header_link_text"> 
        View 
       </th> 
       <th class="entity_record_table_header_link_text"> 
        Delete 
       </th> 
      </tr> 
      @{ 
       String[] rowDisplay = { "entity_record_row_display1", "entity_record_row_display2" }; 
       String currentClass = "entity_record_row_display1"; 
       int count = 0; 
      } 

      @foreach (var item in Model) 
      { 

       count++; 
       currentClass = rowDisplay[count % 2]; 

       <tr class="@(currentClass)"> 
        <td class="entity_record_table_item"> 
         @Html.DisplayFor(modelItem => item.DiscountCard.CardName) 
        </td> 
        <td class="entity_record_table_link"> 
         @Ajax.ActionLink(" ", "Edit", new { id = item.CustomerDiscountCardID }, 
         new AjaxOptions 
          { 
           HttpMethod = "get", 
           InsertionMode = InsertionMode.Replace, 
           UpdateTargetId = "targetDiv" 
          } 
         , new { @class = "entity_record_edit" }) 
        </td> 
        <td class="entity_record_table_link"> 
         @Ajax.ActionLink(" ", "Details", new { id = item.CustomerDiscountCardID }, 
           new AjaxOptions 
           { 
            HttpMethod = "get", 
            InsertionMode = InsertionMode.Replace, 
            UpdateTargetId = "targetCustomerDiscountCardList" 
           } 
         , new { @class = "entity_record_view" }) 
        </td> 
        <td class="entity_record_table_link"> 
         @Ajax.ActionLink(" ", "Delete", new { id = item.CustomerDiscountCardID }, 
           new AjaxOptions 
           { 
            HttpMethod = "get", 
            InsertionMode = InsertionMode.Replace, 
            UpdateTargetId = "targetCustomerDiscountCardList" 
           } 
         , new { @class = "entity_record_delete" }) 
        </td> 
       </tr> 

      } 

     </table> 
    </div> 

</div> 

所以當剃刀發動機渲染此局部視圖礦山和執行下列指令

item.DiscountCard.CardName 

我得到DicountCard爲空，我不能夠明白是什麼原因造成這是空任何一個可以請幫我 這個。 非常感謝。

Answer 1

問題是，DiscountCard真的是爲空。當你獲取的物品，你使用Select創建一個新的類出值的子集：

  Select(c => new 
      { 
       DiscountCardID = c.DiscountCardID, 
       CustomerID = c.CustomerID, 
       IssueDate = c.IssueDate, 
       ExpiryDate = c.ExpiryDate, 
       CustomerDiscountCardID = c.CustomerDiscountCardID 
      } 
      ).ToList().Select(c => new CustomerDiscountCard 
      { 
       DiscountCardID = c.DiscountCardID, 
       CustomerID = c.CustomerID, 
       IssueDate = c.IssueDate, 
       ExpiryDate = c.ExpiryDate, 
       CustomerDiscountCardID = c.CustomerDiscountCardID 

      }) 

首先，你在做什麼是重複的。沒有理由選擇匿名對象，將其轉換爲列表，然後選擇具有相同數據的真實類實例。只需直接選擇的類的實例，即：

  Select(c => new CustomerDiscountCard 
      { 
       DiscountCardID = c.DiscountCardID, 
       CustomerID = c.CustomerID, 
       IssueDate = c.IssueDate, 
       ExpiryDate = c.ExpiryDate, 
       CustomerDiscountCardID = c.CustomerDiscountCardID 

      }) 

其次，你永遠不設置DiscountCard的值，只有DiscountCardId。當你創建一個像這樣的新實例時，它不是而是附加到你的上下文，並且沒有辦法獲取或檢索這個相關的值。這給我們帶來了...

第三，你爲什麼選擇任何東西？首先使用可枚舉的CustomerDiscountCard，然後選擇一個可枚舉的新實例CustomerDiscountCard。這樣做的唯一的事情是打破這些項目的附件到你的上下文，有效地殺死任何懶惰加載任何東西的能力。

UPDATE

只是將其更改爲：

var model = db.CustomerDiscountCards.Include(d => d.DiscountCard). 
      OrderBy(c => c.DiscountCard.CardName). 
      Where(c => (c.DiscountCard.CardName.Contains(searchTerm))). 
      ToPagedList(page, 4);