public static class ConcurrentDictionaryExtensions
    {
        public static TValue GetOrAdd<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, Func<TKey, TValue> valueFactory
        )
        {
            return @this.GetOrAdd(key,
                (k) => new Lazy<TValue>(() => valueFactory(k))
            ).Value;
        }

        public static TValue AddOrUpdate<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, Func<TKey, TValue> addValueFactory,
            Func<TKey, TValue, TValue> updateValueFactory
        )
        {
            return @this.AddOrUpdate(key,
                (k) => new Lazy<TValue>(() => addValueFactory(k)),
                (k, currentValue) => new Lazy<TValue>(
                    () => updateValueFactory(k, currentValue.Value)
                )
            ).Value;
        }

        public static bool TryGetValue<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, out TValue value
        )
        {
            value = default(TValue);

            var result = @this.TryGetValue(key, out Lazy<TValue> v);

            if (result) value = v.Value;

            return result;
        }

        // this overload may not make sense to use when you want to avoid
        //  the construction of the value when it isn't needed
        public static bool TryAdd<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, TValue value
        )
        {
            return @this.TryAdd(key, new Lazy<TValue>(() => value));
        }

        public static bool TryAdd<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, Func<TKey, TValue> valueFactory
        )
        {
            return @this.TryAdd(key,
                new Lazy<TValue>(() => valueFactory(key))
            );
        }

        public static bool TryRemove<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, out TValue value
        )
        {
            value = default(TValue);

            if (@this.TryRemove(key, out Lazy<TValue> v))
            {
                value = v.Value;
                return true;
            }
            return false;
        }

        public static bool TryUpdate<TKey, TValue>(
            this ConcurrentDictionary<TKey, Lazy<TValue>> @this,
            TKey key, Func<TKey, TValue, TValue> updateValueFactory
        )
        {
            if (!@this.TryGetValue(key, out Lazy<TValue> existingValue))
                return false;

            return @this.TryUpdate(key,
                new Lazy<TValue>(
                    () => updateValueFactory(key, existingValue.Value)
                ),
                existingValue
            );
        }
    }

    public static class YeKe
    {
        public const char ArabicYeChar = (char)1610;
        public const char PersianYeChar = (char)1740;

        public const char ArabicKeChar = (char)1603;
        public const char PersianKeChar = (char)1705;

        public static string ApplyCorrectYeKe(this object data)
        {
            return data == null ? null : ApplyCorrectYeKe(data.ToString());
        }

        public static string ApplyCorrectYeKe(this string data)
        {
            return string.IsNullOrWhiteSpace(data) ?
                        string.Empty :
                        data.Replace(ArabicYeChar, PersianYeChar).Replace(ArabicKeChar, PersianKeChar).Trim();
        }

        public static void ApplyCorrectYeKe(this DbCommand command)
        {
            command.CommandText = command.CommandText.ApplyCorrectYeKe();

            foreach (DbParameter parameter in command.Parameters)
            {
                switch (parameter.DbType)
                {
                    case DbType.AnsiString:
                    case DbType.AnsiStringFixedLength:
                    case DbType.String:
                    case DbType.StringFixedLength:
                    case DbType.Xml:
                        parameter.Value =   parameter.Value is DBNull ? parameter.Value : parameter.Value.ApplyCorrectYeKe();
                        break;
                }
            }
        }
    }

using System.Collections.Generic;
namespace CustomerOrdersSample.Domain
{
   public class Customer
   {
       public virtual int Id { get; set; }
       public virtual string Name { get; set; }
       public virtual IList<Order> Orders { get; set; }
   }
}

using System;
using System.Collections.Generic;
namespace CustomerOrdersSample.Domain
{
   public class Order
   {
       public virtual int Id { get; set; }
       public virtual DateTime OrderDate { set; get; }
       public virtual Customer Customer { get; set; }
       public virtual IList<OrderItem> OrderItems { set; get; }
   }
}

namespace CustomerOrdersSample.Domain
{
   public class OrderItem
   {
       public virtual int Id { get; set; }
       public virtual Product Product { get; set; }
       public virtual int Quntity { get; set; }
       public virtual Order Order { set; get; }
   }
}

namespace CustomerOrdersSample.Domain
{
   public class Product
   {
       public virtual int Id { set; get; }
       public virtual string Name { get; set; }
       public virtual decimal UnitPrice { get; set; }
   }
}

    create table Customers (
      CustomerId INT IDENTITY NOT NULL,
      Name NVARCHAR(255) null,
      primary key (CustomerId)
   )

   create table Orders (
      OrderId INT IDENTITY NOT NULL,
      OrderDate DATETIME null,
      CustomerId INT null,
      primary key (OrderId)
   )

   create table OrderItems (
      OrderItemId INT IDENTITY NOT NULL,
      Quntity INT null,
      ProductId INT null,
      OrderId INT null,
      primary key (OrderItemId)
   )

   create table Products (
      ProductId INT IDENTITY NOT NULL,
      Name NVARCHAR(255) null,
      UnitPrice NUMERIC(19,5) null,
      primary key (ProductId)
   )

   alter table Orders
       add constraint fk_Customer_Order
       foreign key (CustomerId)
       references Customers

   alter table OrderItems
       add constraint fk_Product_OrderItem
       foreign key (ProductId)
       references Products

   alter table OrderItems
       add constraint fk_Order_OrderItem
       foreign key (OrderId)
       references Orders

SET IDENTITY_INSERT [Customers] ON;
GO
INSERT INTO [Customers] ([CustomerId],[Name]) VALUES (1,N'Customer1');
GO
SET IDENTITY_INSERT [Customers] OFF;
GO
SET IDENTITY_INSERT [Products] ON;
GO
INSERT INTO [Products] ([ProductId],[Name],[UnitPrice]) VALUES (1,N'Product1',1000.00000);
GO
INSERT INTO [Products] ([ProductId],[Name],[UnitPrice]) VALUES (2,N'Product2',2000.00000);
GO
INSERT INTO [Products] ([ProductId],[Name],[UnitPrice]) VALUES (3,N'Product3',3000.00000);
GO
SET IDENTITY_INSERT [Products] OFF;
GO
SET IDENTITY_INSERT [Orders] ON;
GO
INSERT INTO [Orders] ([OrderId],[OrderDate],[CustomerId]) VALUES (1,{ts '2011-01-07 11:25:20.000'},1);
GO
SET IDENTITY_INSERT [Orders] OFF;
GO
SET IDENTITY_INSERT [OrderItems] ON;
GO
INSERT INTO [OrderItems] ([OrderItemId],[Quntity],[ProductId],[OrderId]) VALUES (1,10,1,1);
GO
INSERT INTO [OrderItems] ([OrderItemId],[Quntity],[ProductId],[OrderId]) VALUES (2,5,2,1);
GO
INSERT INTO [OrderItems] ([OrderItemId],[Quntity],[ProductId],[OrderId]) VALUES (3,20,3,1);
GO
SET IDENTITY_INSERT [OrderItems] OFF;
GO

var list = session.QueryOver<Customer>().List();

foreach (var customer in list)
{
      foreach (var order in customer.Orders)
      {
          foreach (var orderItem in order.OrderItems)
          {
                Console.WriteLine("{0}:{1}:{2}", customer.Name, order.OrderDate, orderItem.Product.Name);
           }
       }
}

Customer1:2011/01/07 11:25:20 :Product1
Customer1:2011/01/07 11:25:20 :Product2
Customer1:2011/01/07 11:25:20 :Product3

var list = session
                   .QueryOver<Customer>()
                   .Fetch(c => c.Orders).Eager
                   .Fetch(c => c.Orders.First().OrderItems).Eager
                   .Fetch(c => c.Orders.First().OrderItems.First().Product).Eager
                   .List();

foreach (var customer in list)
{
     foreach (var order in customer.Orders)
     {
           foreach (var orderItem in order.OrderItems)
           {
               Console.WriteLine("{0}:{1}:{2}", customer.Name, order.OrderDate, orderItem.Product.Name);
            }
      }
}

...
.TransformUsing(NHibernate.Transform.Transformers.DistinctRootEntity)
.List();

var list = session
                   .Query()
                   .FetchMany(c => c.Orders)
                   .ThenFetchMany(o => o.OrderItems)
                   .ThenFetch(p => p.Product)
                   .ToList();