Test-ModuleManifest : The specified module 'D:\Entity Framework Samples\EF Sample 02\packages\EntityFramework.5.0.0\tools\EntityFramework.psd1' was not loaded because no valid module file was found in any module directory.
At D:\Entity Framework Samples\EF Sample 02\packages\EntityFramework.5.0.0\tools\init.ps1:14 char:34
+ $thisModule = Test-ModuleManifest <<<<  (Join-Path $toolsPath $thisModuleManifest)
    + CategoryInfo          : ResourceUnavailable: (D:\Entity Framework Samples\E...yFramework.psd1:String) [Test-ModuleManifest], FileNotFoundException
    + FullyQualifiedErrorId : Modules_ModuleNotFound,Microsoft.PowerShell.Commands.TestModuleManifestCommand
 
Import-Module : Cannot bind argument to parameter 'Name' because it is null.
At D:\Entity Framework Samples\EF Sample 02\packages\EntityFramework.5.0.0\tools\init.ps1:31 char:18
+     Import-Module <<<<  $thisModule
    + CategoryInfo          : InvalidData: (:) [Import-Module], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.ImportModuleCommand

The term 'enable-migrations' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:18
+ enable-migrations <<<< 
    + CategoryInfo          : ObjectNotFound: (enable-migrations:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

Id                             Version              Description/Release Notes                                                                                                                                                                                      
--                             -------              -------------------------                                                                                                                                                                                      
EntityFramework                5.0.0                Entity Framework is Microsoft's recommended data access technology for new applications.

about_EntityFramework.help.txt
EntityFramework.PowerShell.dll
EntityFramework.PowerShell.Utility.dll
EntityFramework.PS3.psd1
EntityFramework.psd1
EntityFramework.psm1
init.ps1
install.ps1
migrate.exe
Redirect.config
Redirect.VS11.config

public class Page
    {
        public virtual int Id { get; set; }
        public virtual string Title { get; set; }
        public virtual DateTime? CreatedDate { get; set; }
        public virtual DateTime? ModifiedDate { get; set; }
        public virtual string Body { get; set; }
        public virtual string Keyword { get; set; }
        public virtual string Description { get; set; }
        public virtual string Status { get; set; }
        public virtual bool? CommentStatus { get; set; }
        public virtual int? Order { get; set; }
        public virtual User User { get; set; }
        public virtual User EditedByUser { get; set; }
        public virtual ICollection<Comment> Comments { get; set; }
        public virtual int? ParentId { get; set; }
        public virtual Page Parent { get; set; }
        public virtual ICollection<Page> Children { get; set; }
    }

this._pages.ToList().Where(page => page.Parent == null).ToList();

SELECT 
[Extent1].[Id] AS [Id], 
[Extent1].[Title] AS [Title], 
[Extent1].[CreatedDate] AS [CreatedDate], 
[Extent1].[ModifiedDate] AS [ModifiedDate], 
[Extent1].[Body] AS [Body], 
[Extent1].[Keyword] AS [Keyword], 
[Extent1].[Description] AS [Description], 
[Extent1].[Status] AS [Status], 
[Extent1].[CommentStatus] AS [CommentStatus], 
[Extent1].[Order] AS [Order], 
[Extent1].[ParentId] AS [ParentId], 
[Extent2].[Id] AS [Id1], 
[Extent2].[Title] AS [Title1], 
[Extent2].[CreatedDate] AS [CreatedDate1], 
[Extent2].[ModifiedDate] AS [ModifiedDate1], 
[Extent2].[Body] AS [Body1], 
[Extent2].[Keyword] AS [Keyword1], 
[Extent2].[Description] AS [Description1], 
[Extent2].[Status] AS [Status1], 
[Extent2].[CommentStatus] AS [CommentStatus1], 
[Extent2].[Order] AS [Order1], 
[Extent2].[ParentId] AS [ParentId1], 
[Extent2].[User_Id] AS [User_Id], 
[Extent2].[EditedByUser_Id] AS [EditedByUser_Id], 
[Extent1].[User_Id] AS [User_Id1], 
[Extent1].[EditedByUser_Id] AS [EditedByUser_Id1]
FROM  [dbo].[Pages] AS [Extent1]
LEFT OUTER JOIN [dbo].[Pages] AS [Extent2] ON [Extent1].[ParentId] = [Extent2].[Id

Null Is Evil. What’s the Best Alternative? Null. 

Work effectively without null references 

WITH cteLead
AS
(
SELECT SalesOrderID,SalesOrderDetailID,OrderQty,
       ROW_NUMBER() OVER (PARTITION BY SalesOrderID 
                          ORDER BY SalesOrderDetailID) AS sn
FROM TestLead_LAG
WHERE
SalesOrderID IN (43670, 43669, 43667, 43663)
)
SELECT m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty,
       COALESCE(sLead1.SalesOrderDetailID, 0) as leadvalue1,
       COALESCE(sLead2.SalesOrderDetailID, 0) as leadvalue2,
       COALESCE(sLag1.SalesOrderDetailID, 0) as lagvalue2,
       COALESCE(sLag2.SalesOrderDetailID, 0) as lagvalue2
FROM cteLead AS m
LEFT OUTER JOIN cteLead AS sLead1
ON m.sn = sLead1.sn - 1
AND m.SalesOrderID = sLead1.SalesOrderID 
LEFT OUTER JOIN cteLead AS sLead2
ON m.sn = sLead2.sn - 2
AND m.SalesOrderID = sLead2.SalesOrderID 
LEFT OUTER JOIN cteLead AS sLag1
ON m.sn = sLag1.sn + 1
AND m.SalesOrderID = sLag1.SalesOrderID 
LEFT OUTER JOIN cteLead AS sLag2
ON m.sn = sLag2.sn + 2
AND m.SalesOrderID = sLag2.SalesOrderID 
ORDER BY m.SalesOrderID, m.SalesOrderDetailID, m.OrderQty;

SELECT s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty,
       Lead(SalesOrderDetailID, 1, 0) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LeadValue1,
       LAG(SalesOrderDetailID, 1, 0) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LAGValue1,
       Lead(SalesOrderDetailID, 2, 0) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LeadValue2,
       LAG(SalesOrderDetailID, 2, 0) OVER (PARTITION BY SalesOrderID ORDER BY SalesOrderDetailID) LAGValue2,
FROM TestLead_LAG s
WHERE SalesOrderID IN (43670, 43669, 43667, 43663)
ORDER BY s.SalesOrderID,s.SalesOrderDetailID,s.OrderQty