c# – NullReferenceException对有效的操作

var firstQuery = 
    from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
    join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
    select new
    {
        ContPrice = conts.Price,RoomPrice = rooms.Price
        IDs = rooms.ID
    };

foreach (var t in firstQuery)
{
    t.RoomPrice  = t.ContPrice;
}

然后我做一些操作(更新价格),最后我使用ID作为第二个查询.该第二个查询不包含这些ID.我以这种方式实现了这个问题：

var myIDs = firstQuery.Select(cr => cr.IDs).ToList();

而我的第二个查询是：

var secondQuery = 
    from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0) 
    where !myIDs.Contains(rooms.fldID)                                   
    join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
    select new
    {
       RoomPrice = conts.fldPrice,IDs = rooms.ID
    };

当我以调试器模式运行此代码并达到此行时：

var myIDs = firstQuery.Select(cr => cr.IDs).ToList();

…提出了一个例外：

NullReferenceException
Object reference not set to an instance of an object.

似乎它与第二个查询有关,因为当我将第二个查询传递给一个单独的方法,并将ID传递给它时,一切都很完美,但是我不明白为什么它应该考虑一些在该变量之后编写的查询初始化.

整个代码是：

var calcDate = DateTime.Now.AddDays(-1);

var firstQuery = 
    from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0)
    join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
    where conts.date == calcDate
    select new
    {
        ContPrice = conts.Price,RoomPrice = rooms.Price
        IDs = rooms.ID
    };

foreach (var t in firstQuery)
{
    t.RoomPrice = t.ContPrice;
}

var myIDs = firstQuery.Select(cr => cr.IDs).ToList();


var secondQuery = 
    from rooms in myEntityContext.Room.Where(t => t.fldClosed == 0) 
    where !myIDs.Contains(rooms.fldID)                                   
    join conts in myEntityContext.Cont on rooms.ID equals conts.ItemID
    where conts.date == calcDate && conts.Code = "01"
    select new
    {
       RoomPrice = conts.fldPrice,IDs = rooms.ID
    };

foreach (var t in secondQuery)
{
    ContPrice = Conts.Price,RoomPrice = Rooms.Price
}

myEntityContext.SaveChanges();

这是我的堆栈跟踪,如果它是有用的：

Financial.UI.dll!Financial.UI.Services.Hotels.HotelServiceProxy.CalcProxy.DoCalc(System.DateTime calcDate) Line 5055    C#
Financial.UI.dll!Financial.UI.Pages.Hotel.NightsCalculationPage.CallbackMethod_DoCalc() Line 65 + 0x37 bytes    C#
[Native to Managed Transition]  
Web.UI.dll!Web.UI.SystemCallback.ProcessCallback() Line 228 + 0x3b bytes    C#
Web.UI.dll!Web.UI.SystemCallbackHandler.ProcessRequest(System.Web.HttpContext context) Line 68 + 0x12 bytes C#
System.Web.dll!System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() + 0x156 bytes    
System.Web.dll!System.Web.HttpApplication.ExecuteStep(System.Web.HttpApplication.IExecutionStep step,ref bool completedSynchronously) + 0x46 bytes 
System.Web.dll!System.Web.HttpApplication.PipelineStepManager.ResumeSteps(System.Exception error) + 0x342 bytes 
System.Web.dll!System.Web.HttpApplication.BeginProcessRequestNotification(System.Web.HttpContext context,System.AsyncCallback cb) + 0x60 bytes 
System.Web.dll!System.Web.HttpRuntime.ProcessRequestNotificationPrivate(System.Web.Hosting.IIS7WorkerRequest wr,System.Web.HttpContext context) + 0xbb bytes   
System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(System.IntPtr rootedObjectsPointer,System.IntPtr nativeRequestContext,System.IntPtr moduleData,int flags) + 0x1f3 bytes   
System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(System.IntPtr rootedObjectsPointer,int flags) + 0x1f bytes  
[Native to Managed Transition]  
[Managed to Native Transition]  
System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(System.IntPtr rootedObjectsPointer,int flags) + 0x350 bytes   
System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(System.IntPtr rootedObjectsPointer,int flags) + 0x1f bytes  
[Appdomain Transition]