<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>

<script runat="server">

  void PopulateNode(Object sender, TreeNodeEventArgs e)
  {

    // Call the appropriate method to populate a node at a particular level.
    switch(e.Node.Depth)
    {
      case 0:
        // Populate the first-level nodes.
        PopulateCategories(e.Node);
        break;
      case 1:
        // Populate the second-level nodes.
        PopulateProducts(e.Node);
        break;
      default:
        // Do nothing.
        break;
    }
    
  }

  void PopulateCategories(TreeNode node)
  {
    
    // Query for the product categories. These are the values
    // for the second-level nodes.
    DataSet ResultSet = RunQuery("Select CategoryID, CategoryName From Categories");

    // Create the second-level nodes.
    if(ResultSet.Tables.Count > 0)
    {
    
      // Iterate through and create a new node for each row in the query results.
      // Notice that the query results are stored in the table of the DataSet.
      foreach (DataRow row in ResultSet.Tables[0].Rows)
      {
        
        // Create the new node. Notice that the CategoryId is stored in the Value property 
        // of the node. This will make querying for items in a specific category easier when
        // the third-level nodes are created. 
        TreeNode newNode = new TreeNode();
        newNode.Text = row["CategoryName"].ToString(); 
        newNode.Value = row["CategoryID"].ToString();        

        // Set the PopulateOnDemand property to true so that the child nodes can be 
        // dynamically populated.
        newNode.PopulateOnDemand = true;
        
        // Set additional properties for the node.
        newNode.SelectAction = TreeNodeSelectAction.Expand;
        
        // Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(newNode);
        
      }
      
    }
    
  }

  void PopulateProducts(TreeNode node)
  {

    // Query for the products of the current category. These are the values
    // for the third-level nodes.
    DataSet ResultSet = RunQuery("Select ProductName From Products Where CategoryID=" + node.Value);

    // Create the third-level nodes.
    if(ResultSet.Tables.Count > 0)
    {
    
      // Iterate through and create a new node for each row in the query results.
      // Notice that the query results are stored in the table of the DataSet.
      foreach (DataRow row in ResultSet.Tables[0].Rows)
      {
      
        // Create the new node.
        TreeNode NewNode = new TreeNode(row["ProductName"].ToString());
        
        // Set the PopulateOnDemand property to false, because these are leaf nodes and
        // do not need to be populated.
        NewNode.PopulateOnDemand = false;
        
        // Set additional properties for the node.
        NewNode.SelectAction = TreeNodeSelectAction.None;
        
        // Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(NewNode);
        
      }
      
    }

  }

  DataSet RunQuer