# Server-side Binding

To load data on-demand using server side code:

* Query the root node data, i.e. for the nodes that the user will see first. When using self-referential hierarchical databases this can be done by querying for nodes where the "parent id" is null.

* Iterate the root node data and add new node objects for each record. Assign to the **Text** property the data column representing readable text and assign the column containing unique identifiers to the **Value** property of each node. The **Value** property will be used later as a parent id when opening a node. Set the Node **ExpandMode** property to **ServerSide;** expanding a node will cause a postback to the server. During the postback, the server **NodeExpand** event handler will have a chance to fire.

* Create a **NodeExpand** event handler. This event will pass a reference to the clicked-on node as a parameter. Use the node **Value** property to query for all child nodes of this parent node.

* Iterate the child nodes, again populating the **Text** and **Value** property of each node. Set each child node's **ExpandMode** property to **ServerSide**. Set the **ExpandNode** for the clicked-on, parent node to **ClientSide** the child nodes for this parent node have already been loaded with data so there is no need to return to the server. Also, set the **Expanded** property of the parent node to **True**.

The example below loads data from the Access Database.mdb database. This database can be found in the RadControls installation directory under *Live Demos\App_Data*. Any data that has ID, Parent ID and text column data would work in this scenario. In this example the **LoadRootNodes**() method loads only the node called "Root". When the user clicks that node the first time, the **NodeExpand** event is fired:

* The data for the child nodes of the parent "Root" are retrieved.

* Nodes are created for each record and attached as child nodes to the parent node. The **ExpandMode** property of each child node is set to **ServerSide**.

* The parent node "Root" **Expanded** property is set to **True**, opening the node to display the child nodes.

* The parent node "Root" **ExpandMode** property is set to **ClientSide** because the child nodes have already been loaded.

The same general pattern for NodeExpand is repeated when the user clicks a node that has not yet been expanded.

> caption

![RadTreeView Server-Side Load on Demand](https://www.telerik.com/products/aspnet-ajax/documentation/assets/f0a3fa0a6cd7e1fe76683a04b763fd57/treeview_loadondemandserverside.png)

```C#
using System;
using System.Data;
using System.Data.OleDb;
using Telerik.Web.UI;

namespace RadTreeView_DataBindDataTable
{    
    public partial class _Default : System.Web.UI.Page    
    {        
        protected void Page_Load(object sender, EventArgs e)        
        {            
            if (!IsPostBack)            
            {                
                LoadRootNodes(RadTreeView1);            
            }        
        }
        private void LoadRootNodes(RadTreeView treeView)        
        {            
            const string sql = "Select Name, ItemID from Items where ParentID IS NULL";            
            OleDbConnection connection = new OleDbConnection(Properties.Settings.Default.AccessConnection);            
            OleDbDataAdapter adapter = new OleDbDataAdapter(sql, connection);            
            DataTable dataTable = new DataTable();            
            adapter.Fill(dataTable);

            foreach (DataRow row in dataTable.Rows)            
            {                
                RadTreeNode node = new RadTreeNode();                
                node.Text = row["Name"].ToString();               
                node.Value = row["ItemID"].ToString();                
                node.ExpandMode = TreeNodeExpandMode.ServerSide;                
                RadTreeView1.Nodes.Add(node);            
            }        
        }

        protected void RadTreeView1_NodeExpand(object sender, RadTreeNodeEventArgs e)        
        {            
            const string sql =@"SELECT Items.ItemID AS NodeId, Items.Name AS NodeText, COUNT(Children.ItemID) AS ChildCount FROM Items LEFT JOIN Items As Children ON Items.ItemID = Children.ParentId WHERE Items.ParentId = @parentId GROUP BY Items.ItemID, Items.Name";
            OleDbConnection connection = new OleDbConnection(Properties.Settings.Default.AccessConnection);           
            OleDbDataAdapter adapter = new OleDbDataAdapter(sql, connection);            
            adapter.SelectCommand.Parameters.AddWithValue("parentId", e.Node.Value);     
            DataTable dataTable = new DataTable();            
            adapter.Fill(dataTable);

            foreach (DataRow row in dataTable.Rows)
            {                
                RadTreeNode node = new RadTreeNode();
                node.Text = row["NodeText"].ToString();
                node.Value = row["NodeId"].ToString();
                if (Convert.ToInt32(row["ChildCount"]) > 0)        
                {
                    node.ExpandMode = TreeNodeExpandMode.ServerSide;
                }                
                e.Node.Nodes.Add(node);
            }

            e.Node.Expanded = true;
            e.Node.ExpandMode = TreeNodeExpandMode.ClientSide;
        } 
    }
}
```

```VB.NET
Imports System
Imports System.Data
Imports System.Data.OleDb
Imports Telerik.Web.UI
Namespace RadTreeView_DataBindDataTable
    Partial Public Class _Default
        Inherits System.Web.UI.Page
        Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
            If Not IsPostBack Then
                LoadRootNodes(RadTreeView1)
            End If
        End Sub
        Private Sub LoadRootNodes(ByVal treeView As RadTreeView)
            Const sql As String = "Select Name, ItemID from Items where ParentID IS NULL"
            Dim connection As New OleDbConnection(Properties.Settings.[Default].AccessConnection)
            Dim adapter As New OleDbDataAdapter(sql, connection)
            Dim dataTable As New DataTable()
            adapter.Fill(dataTable)
            For Each row As DataRow In dataTable.Rows
                Dim node As New RadTreeNode()
                node.Text = row("Name").ToString()
                node.Value = row("ItemID").ToString()
                node.ExpandMode = TreeNodeExpandMode.ServerSide
                RadTreeView1.Nodes.Add(node)
            Next
        End Sub
        Protected Sub RadTreeView1_NodeExpand(ByVal sender As Object, ByVal e As RadTreeNodeEventArgs)
            Const sql As String = "SELECT Items.ItemID AS NodeId, Items.Name AS NodeText, COUNT(Children.ItemID) AS ChildCount FROM Items LEFT JOIN Items As Children ON Items.ItemID = Children.ParentId WHERE Items.ParentId = @parentId GROUP BY Items.ItemID, Items.Name"
            Dim connection As New OleDbConnection(Properties.Settings.[Default].AccessConnection)
            Dim adapter As New OleDbDataAdapter(sql, connection)
            adapter.SelectCommand.Parameters.AddWithValue("parentId", e.Node.Value)
            Dim dataTable As New DataTable()
            adapter.Fill(dataTable)
            For Each row As DataRow In dataTable.Rows
                Dim node As New RadTreeNode()
                node.Text = row("NodeText").ToString()
                node.Value = row("NodeId").ToString()
                If Convert.ToInt32(row("ChildCount")) > 0 Then
                    node.ExpandMode = TreeNodeExpandMode.ServerSide
                End If
                e.Node.Nodes.Add(node)
            Next
            e.Node.Expanded = True
            e.Node.ExpandMode = TreeNodeExpandMode.ClientSide
        End Sub
    End Class
End Namespace
```