模型綁定DBContext部署在頁面加載

Question

我一直在努力理解爲什麼我添加一個.Skip（）和.Take（）linq方法查詢時，我得到一個DBContext處置錯誤。我有一個運行良好的版本，沒有上面提到的方法，只是無法掌握造成差異的原因。

下面是兩種方法，即返回數據模型綁定GridView的選擇方法：

// This is the method that causes the DBContext disposed exception 

      public IQueryable<ProductCategory> GetCategoriesByPage(int pageNumber, int pageSize) 
     { 
      using (var dataModel = new MagicDayEntities()) 
      { 
       var pagedCategories = (from categories in dataModel.ProductCategories 
             orderby categories.CategoryName ascending 
             select categories) 
         .Skip((pageSize - 1) * pageNumber) 
         .Take(pageSize); 
       pagedCategories.ToList().AsQueryable(); 
       return pagedCategories; 
      } 
     } 

//This method returns the data properly without error 

     public IQueryable<ProductCategory> GetAllCategories() 
     { 
      using (var dataModel = new MagicDayEntities()) 
      { 
       var allCategories = (from categories in dataModel.ProductCategories 
            orderby categories.CategoryName ascending 
            select categories) 
            .ToList() 
            .AsQueryable(); 
       return allCategories; 
      } 
     } 

在我所知的ToList（）應強制查詢運行，並克服了懶惰負荷的行爲，使DbContext處於「使用」語句中，這是一項要求。

以下是異常的詳細信息：

The operation cannot be completed because the DbContext has been disposed. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidOperationException: The operation cannot be completed because the DbContext has been disposed. 

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. 

Stack Trace: 


[InvalidOperationException: The operation cannot be completed because the DbContext has been disposed.] 
    System.Data.Entity.Internal.LazyInternalContext.InitializeContext() +4249201 
    System.Data.Entity.Internal.Linq.DbQueryProvider.Execute(Expression expression) +40 
    System.Linq.Queryable.Count(IQueryable`1 source) +196 
    System.Web.UI.WebControls.QueryableHelpers.CountHelper(IQueryable`1 queryable) +48 

[TargetInvocationException: Exception has been thrown by the target of an invocation.] 
    System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) +0 
    System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments) +160 
    System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +101 
    System.Web.UI.WebControls.ModelDataSourceView.ProcessSelectMethodResult(DataSourceSelectArguments arguments, DataSourceSelectResultProcessingOptions selectResultProcessingOptions, ModelDataMethodResult result) +249 
    System.Web.UI.WebControls.ModelDataSourceView.GetSelectMethodResult(DataSourceSelectArguments arguments) +92 
    System.Web.UI.WebControls.ModelDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +15 
    System.Web.UI.DataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) +22 
    System.Web.UI.WebControls.ModelDataSourceView.Select(DataSourceSelectArguments arguments, DataSourceViewSelectCallback callback) +80 
    System.Web.UI.WebControls.DataBoundControl.PerformSelect() +143 
    System.Web.UI.WebControls.BaseDataBoundControl.DataBind() +74 
    System.Web.UI.WebControls.GridView.DataBind() +9 
    System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() +114 
    System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls() +75 
    System.Web.UI.Control.EnsureChildControls() +92 
    System.Web.UI.Control.PreRenderRecursiveInternal() +42 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Control.PreRenderRecursiveInternal() +160 
    System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +883 


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.6.1586.0 

有人能幫助我，並闡明此異常的原因一些輕？ 在此先感謝。 彼得

Answer 1

通過調用ToList執行查詢：

pagedCategories.ToList().AsQueryable(); 

然後忽略結果，當您的視圖結合，使其恢復原來的查詢，將被執行：

return pagedCategories; 

更改返回列表：

return pagedCategories.ToList().AsQueryable(); 

I 'd也建議將退貨類型更改爲IEnumerable<ProductCategory>並將呼叫移除至AsQueryable。這樣做沒有任何意義。