延迟加载与实体框架5.0不工作的相关实体
本文关键字：实体 工作 框架 延迟加载 | 更新日期: 2023-09-27 18:04:29
我在我的项目中首先使用实体框架5使用数据库。我相信有一些问题在延迟加载值在外键虚拟字段，我已经尝试了所有可能的方法，但我不能解决这个问题，到目前为止。
详情如下:
我有一个CustomerDiscountCardController索引方法如下:
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;
}
我的数据上下文类如下:
public OnlineFoodOrderingEntities2()
: base("name=OnlineFoodOrderingEntities2")
{
this.Configuration.LazyLoadingEnabled = true;
this.Configuration.ProxyCreationEnabled = true;
}
//Entities class code....
}
自动生成的CustomerDiscountCard类如下所示:
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的部分布局
布局代码如下:
@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razor引擎渲染我的部分视图并执行以下命令
时item.DiscountCard.CardName
我得到DicountCard为空，我无法理解是什么原因导致这是空的，任何人都可以帮助我这个。
问题是DiscountCard实际上是 null。当您获取项目时，您正在使用Select从值子集中创建一个新类:
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，你所做的是重复的。没有理由选择一个匿名对象，强制转换为列表，然后选择一个具有相同数据的真实类实例。直接选择到类实例，即:
Select(c => new CustomerDiscountCard
{
DiscountCardID = c.DiscountCardID,
CustomerID = c.CustomerID,
IssueDate = c.IssueDate,
ExpiryDate = c.ExpiryDate,
CustomerDiscountCardID = c.CustomerDiscountCardID
})
第二，您从未为DiscountCard设置值，仅为DiscountCardId设置值。当您创建这样的新实例时，它是而不是附加到您的上下文，并且无法获取或检索此相关值。这让我们想到……
第三，为什么你首先要选择什么?从CustomerDiscountCard的可枚举对象开始，然后选择新的CustomerDiscountCard实例的可枚举对象。这样做的唯一作用是破坏这些项与上下文的关联，从而有效地消除了延迟加载任何内容的能力。
改成:
var model = db.CustomerDiscountCards.Include( d => d.DiscountCard).
OrderBy(c => c.DiscountCard.CardName).
Where(c => (c.DiscountCard.CardName.Contains(searchTerm))).
ToPagedList(page, 4);