Grid View for ASP.NET Web Forms - How to implement the master-detail functionality with list data sources

C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace EditableDetails {
    public class DataHelper {
        public static List<Parent> CreateMasterData(int masterRowCount) {
            List<Parent> parentList = new List<Parent>();

            for (int i = 0; i < masterRowCount; i++) {
                parentList.Add(new Parent() {
                    ID = i,
                    Name = "Parent" + i.ToString()
                });
            }

            return parentList;
        }

        public static List<Child> CreateChildData(int childRowCount, int maxMasterIndex) {
            List<Child> childList = new List<Child>();
            Random r = new Random();

            for (int i = 0; i < childRowCount; i++) {
                childList.Add(new Child() {
                    ID = i,
                    Name = "Child" + i.ToString(),
                    ParentID = r.Next(maxMasterIndex)
                });
            }

            return childList;
        }
    }

    public class Parent {
        public int ID { get; set; }
        public string Name { get; set; }
    }

    public class Child {
        public int ID { get; set; }
        public string Name { get; set; }
        public int ParentID { get; set; }
    }

}

Visual Basic
Imports System
Imports System.Collections.Generic

Namespace EditableDetails

    Public Class DataHelper

        Public Shared Function CreateMasterData(ByVal masterRowCount As Integer) As List(Of Parent)
            Dim parentList As List(Of Parent) = New List(Of Parent)()
            For i As Integer = 0 To masterRowCount - 1
                parentList.Add(New Parent() With {.ID = i, .Name = "Parent" & i.ToString()})
            Next

            Return parentList
        End Function

        Public Shared Function CreateChildData(ByVal childRowCount As Integer, ByVal maxMasterIndex As Integer) As List(Of Child)
            Dim childList As List(Of Child) = New List(Of Child)()
            Dim r As Random = New Random()
            For i As Integer = 0 To childRowCount - 1
                childList.Add(New Child() With {.ID = i, .Name = "Child" & i.ToString(), .ParentID = r.Next(maxMasterIndex)})
            Next

            Return childList
        End Function
    End Class

    Public Class Parent

        Public Property ID As Integer

        Public Property Name As String
    End Class

    Public Class Child

        Public Property ID As Integer

        Public Property Name As String

        Public Property ParentID As Integer
    End Class
End Namespace

C#
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using DevExpress.Web;
using System.Collections.Generic;
using System.Linq;

namespace EditableDetails {
    public partial class _Default : System.Web.UI.Page {

        public List<Parent> ParentData {
            get {
                if (Session["ParentData"] == null)
                    Session["ParentData"] = DataHelper.CreateMasterData(5);
                return (List<Parent>)Session["ParentData"];
            }
            set {
                Session["ParentData"] = value;
            }
        }

        public List<Child> ChildData {
            get {
                if (Session["ChildData"] == null)
                    Session["ChildData"] = DataHelper.CreateChildData(50, ParentData.Count);
                return (List<Child>)Session["ChildData"];
            }
            set {
                Session["ChildData"] = value;
            }
        }

        protected void Page_Init(object sender, EventArgs e) {
            masterGrid.DataSource = ParentData;
            masterGrid.DataBind();
        }

        protected void detailGrid_BeforePerformDataSelect(object sender, EventArgs e) {
            ASPxGridView detailGrid = (ASPxGridView)sender;
            int id = (int)detailGrid.GetMasterRowKeyValue();

            var result = from q in ChildData
                         where q.ParentID == id
                         select q;

            detailGrid.DataSource = result;
        }


    }


}

Visual Basic
Imports System
Imports System.Data
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls
Imports DevExpress.Web
Imports System.Collections.Generic
Imports System.Linq

Namespace EditableDetails

    Public Partial Class _Default
        Inherits Page

        Public Property ParentData As List(Of Parent)
            Get
                If Session("ParentData") Is Nothing Then Session("ParentData") = DataHelper.CreateMasterData(5)
                Return CType(Session("ParentData"), List(Of Parent))
            End Get

            Set(ByVal value As List(Of Parent))
                Session("ParentData") = value
            End Set
        End Property

        Public Property ChildData As List(Of Child)
            Get
                If Session("ChildData") Is Nothing Then Session("ChildData") = DataHelper.CreateChildData(50, ParentData.Count)
                Return CType(Session("ChildData"), List(Of Child))
            End Get

            Set(ByVal value As List(Of Child))
                Session("ChildData") = value
            End Set
        End Property

        Protected Sub Page_Init(ByVal sender As Object, ByVal e As EventArgs)
            masterGrid.DataSource = ParentData
            masterGrid.DataBind()
        End Sub

        Protected Sub detailGrid_BeforePerformDataSelect(ByVal sender As Object, ByVal e As EventArgs)
            Dim detailGrid As ASPxGridView = CType(sender, ASPxGridView)
            Dim id As Integer = CInt(detailGrid.GetMasterRowKeyValue())
            Dim result = From q In ChildData Where q.ParentID = id Select q
            detailGrid.DataSource = result
        End Sub
    End Class
End Namespace