延迟加载相关实体不与实体框架5.0工作

Question

我使用实体框架5在我的项目中首先使用数据库。我相信在外键虚拟字段中延迟加载值时存在一些问题，并且我尝试了各种方法，但目前为止我无法解决此问题。

下面是详细信息：

我有一个CustomerDiscountCardController指数方法如下：

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; 
     } 

我的数据上下文类看起来如下：

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

} 

我的自动生成的CustomerDiscountCard类看起来如下所示：

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; } 
} 

现在的问题是当我的索引方法被调用Ajax请求返回_CustomerDiscountCard

布局的代码的局部布局是如下：

@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> 

所以当剃刀发动机渲染此局部视图矿山和执行下列指令

item.DiscountCard.CardName 

我得到DicountCard为空，我不能够明白是什么原因造成这是空任何一个可以请帮我 这个。 非常感谢。

Answer 1

问题是，DiscountCard真的是为空。当你获取的物品，你使用Select创建一个新的类出值的子集：

  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，你在做什么是重复的。没有理由选择匿名对象，将其转换为列表，然后选择具有相同数据的真实类实例。只需直接选择的类的实例，即：

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

      }) 

其次，你永远不设置DiscountCard的值，只有DiscountCardId。当你创建一个像这样的新实例时，它不是而是附加到你的上下文，并且没有办法获取或检索这个相关的值。这给我们带来了...

第三，你为什么选择任何东西？首先使用可枚举的CustomerDiscountCard，然后选择一个可枚举的新实例CustomerDiscountCard。这样做的唯一的事情是打破这些项目的附件到你的上下文，有效地杀死任何懒惰加载任何东西的能力。

UPDATE

只是将其更改为：

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