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The DataSet object represents an in-memory database

A single DataSet can contain one or many DataTable objects.  You can define parent/child relationships between the DataTable objects contained in a DataSet. <%@ Page Language="C#" %> <%@ Import Namespace="System.Data" %> <%@ Import Namespace="System.Data.SqlClient" %> <%@ Import Namespace="System.Web.Configuration" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server">     void Page_Load()     {         if (!Page.IsPostBack)             BuildTree();     }     void BuildTree()     {         string connectionString = WebConfigurationManager.ConnectionStrings["Products"].ConnectionString;         SqlConnection con = new SqlConnection(connectionString);         SqlDataAdapter dadCategories = new SqlDataAdapter("SELECT Id,Name FROM ProductCategories", con);         SqlDataAdapter dadProducts = new SqlDataAdapter("SELECT Title,CategoryId FROM Products", con);         DataSet dstProducts = new DataSet();         using (con)         {             con.Open();             dadCategories.Fill(dstProducts, "Categories");             dadProducts.Fill(dstProducts, "Products");         }         dstProducts.Relations.Add("Children", dstProducts.Tables["Categories"].Columns["Id"], dstProducts.Tables["Products"].Columns["CategoryId"]);         foreach (DataRow categoryRow in dstProducts.Tables["Categories"].Rows)         {             string name = (string)categoryRow["Name"];             TreeNode catNode = new TreeNode(name);             TreeView1.Nodes.Add(catNode);             DataRow[] productRows = categoryRow.GetChildRows("Children");             foreach (DataRow productRow in productRows)             {                 string title = (string)productRow["Title"];                 TreeNode productNode = new TreeNode(title);                 catNode.ChildNodes.Add(productNode);             }         }     } </script> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server">     <title>Show DataSet</title> </head> <body>     <form id="form1" runat="server">     <div>     <asp:TreeView         id="TreeView1"         Runat="server" />     </div>     </form> </body> </html> File: Web.config <configuration>   <connectionStrings>     <add name="Products"           connectionString="Data Source=.\SQLEXPRESS;          AttachDbFilename=|DataDirectory|MyDatabase.mdf;Integrated Security=True;User Instance=True" />   </connectionStrings> </configuration>