(în curs de editare)

PASUL 1 . Modificare DAL pentru a folosi LINQ

using System.Linq;

using System.Collections.Generic;
using AdventureWorksModel;


namespace WebApplication3
{
    public class CustomerDataSource
    {
        public static List<Customer> GetCustomers() { 
           using (AdventureWorksLTModel aw = new AdventureWorksLTModel() )
           {
               return GetQuery(aw).OrderBy(c => c.CompanyName).Skip(10).Take(5).ToList();
           }
        }


        public static IQueryable<Customer> GetQuery(AdventureWorksLTModel aw)
        { 
           var query = from c in aw.Customer
                       where c.SalesOrderHeaderes.Sum(s=> s.TotalDue) > 5000
                       select c;

           return query;
        }
    }
}

PASUL 2 . Verificare în SQL Profiler

SELECT TOP (5) 
[Filter2].[CustomerID] AS [CustomerID], 
[Filter2].[Title] AS [Title], 
[Filter2].[FirstName] AS [FirstName], 
[Filter2].[MiddleName] AS [MiddleName], 
[Filter2].[LastName] AS [LastName], 
[Filter2].[Suffix] AS [Suffix], 
[Filter2].[CompanyName] AS [CompanyName], 
[Filter2].[SalesPerson] AS [SalesPerson], 
[Filter2].[EmailAddress] AS [EmailAddress], 
[Filter2].[Phone] AS [Phone]
FROM ( SELECT [Project2].[CustomerID] AS [CustomerID], 
           [Project2].[EmailAddress] AS [EmailAddress], 
           [Project2].[Phone] AS [Phone], 
           [Project2].[Title] AS [Title], 
           [Project2].[FirstName] AS [FirstName], 
           [Project2].[MiddleName] AS [MiddleName], 
           [Project2].[LastName] AS [LastName], 
           [Project2].[Suffix] AS [Suffix], 
           [Project2].[CompanyName] AS [CompanyName], 
           [Project2].[SalesPerson] AS [SalesPerson], 
           [Project2].[C1] AS [C1], 
           row_number() OVER (ORDER BY [Project2].[CompanyName] ASC) AS [row_number]
    FROM ( SELECT 
        [Extent1].[CustomerID] AS [CustomerID], 
        [Extent1].[EmailAddress] AS [EmailAddress], 
        [Extent1].[Phone] AS [Phone], 
        [Extent2].[Title] AS [Title], 
        [Extent2].[FirstName] AS [FirstName], 
        [Extent2].[MiddleName] AS [MiddleName], 
        [Extent2].[LastName] AS [LastName], 
        [Extent2].[Suffix] AS [Suffix], 
        [Extent2].[CompanyName] AS [CompanyName], 
        [Extent2].[SalesPerson] AS [SalesPerson], 
        (SELECT 
            SUM([Project1].[TotalDue]) AS [A1]
            FROM ( SELECT 
                [Extent3].[TotalDue] AS [TotalDue]
                FROM [dbo].[SalesOrderHeader] AS [Extent3]
                WHERE [Extent1].[CustomerID] = [Extent3].[CustomerID]
            )  AS [Project1]) AS [C1]
        FROM  [dbo].[CustomerContactInfo] AS [Extent1]
        INNER JOIN [dbo].[Customer] AS [Extent2] ON [Extent1].[CustomerID] = [Extent2].[CustomerID]
    )  AS [Project2]
    WHERE [Project2].[C1] > cast(5000 as decimal(18))
)  AS [Filter2]
WHERE [Filter2].[row_number] > 10
ORDER BY [Filter2].[CompanyName] ASC