Просмотр исходного текста страницы ASP.NET Tutorial/Data Binding/DropDownList

== Binding ArrayList to asp:DropDownList==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
    Sub Page_Load()
        if Not Page.IsPostBack Then
            Dim items As New ArrayList()
            items.Add("A")
            items.Add("B")
            DropDownList1.DataSource = items
            DropDownList1.DataBind()
        End If
    End Sub
    Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs)
        Label1.Text = DropDownList1.SelectedItem.Text
    End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Show IsPostBack</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    <asp:DropDownList
        id="DropDownList1"
        Runat="server" />
    
    <asp:Button
        id="Button1"
        Text="Select"
        OnClick="Button1_Click" 
        Runat="server" />
    
    <br /><br />
    You selected:
    <asp:Label  
        id="Label1"
        Runat="server" />
    
    </div>
    </form>
</body>
</html></source>
    
   

== Binding to a Data Source==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Declarative DataBinding</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:DropDownList
        id="ddlProducts"
        DataSourceID="srcProducts"
        DataTextField="Title"
        DataValueField="Id"
        Runat="server" />
    <asp:SqlDataSource
        id="srcProducts"
        SelectCommand="SELECT Id, Title FROM Products"
        ConnectionString="<%$ ConnectionStrings:Products %>"
        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></source>
    
   

== Data binding by filling list and drop-down list controls with the results of direct ADO.NET queries==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 
    Inherits="Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>DataSource-based Binding</title>
</head>
<body>
    <div id="pageContent">
        <form id="form1" runat="server">
            <h2>Browse Customers</h2>
            <hr />
            <table><tr>
                <td valign="top"> 
                    <asp:ListBox ID="CustomerList" runat="server" Height="200px" Width="280px" />
                </td>
                <td valign="top"> 
                    <asp:DropDownList runat="server" ID="CountryList" AppendDataBoundItems="True" Width="130px">
                        <asp:ListItem Text="[All]" /> 
                    </asp:DropDownList>            
                    <br />
                    <asp:Button ID="CountriesButton" runat="server" Text="Get countries..." Width="130px"
                        OnClick="CountriesButton_Click" />
                </td>
            </tr></table>
            <hr />
            <asp:Button ID="CustomersButton" runat="server" Text="Get customers..." 
                OnClick="CustomersButton_Click" />
       </form>
   </div>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default : System.Web.UI.Page
{
    protected void CountriesButton_Click(object sender, EventArgs e)
    {
        if (CountryList.Items.Count > 1)
            return;
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
        using (SqlConnection conn = new SqlConnection(connString))
        {
            string cmdText = "SELECT DISTINCT country FROM customers";
            SqlCommand cmd = new SqlCommand(cmdText, conn);
            cmd.Connection.Open();
            using (SqlDataReader reader = cmd.ExecuteReader())
            {
                CountryList.DataSource = reader;
                CountryList.DataTextField = "country";
                CountryList.DataBind();
            }
        }
    }
    protected void CustomersButton_Click(object sender, EventArgs e)
    {
        CustomerList.Items.Clear();
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
        string cmdText1 = "SELECT CustomerID, CompanyName, Country FROM customers";
        string cmdText2 = "SELECT CustomerID, CompanyName, Country FROM customers WHERE country="{0}"";
        string cmdText = cmdText1;
        if (CountryList.SelectedIndex > 0)
            cmdText = String.Format(cmdText2, CountryList.SelectedValue);
        DataSet data = new DataSet();
        SqlDataAdapter adapter = new SqlDataAdapter(cmdText, connString);
        adapter.Fill(data);
        CustomerList.DataMember = "Table";
        CustomerList.DataTextField = "companyname";
        CustomerList.DataValueField = "customerid";
        CustomerList.DataSource = data;
        CustomerList.DataBind();
    }
}</source>
    
   

== Determining the Selected List Item: SelectedIndex, SelectedItem, SelectedValue==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<script runat="server">
    protected void btnSelect_Click(object sender, EventArgs e)
    {
        lblSelectedProduct.Text = ddlProducts.SelectedItem.Text;
    }
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Select Product</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:DropDownList
        id="ddlProducts"
        DataSourceID="srcProducts"
        DataTextField="Title"
        DataValueField="Id"
        Runat="server" />
    <asp:Button
        id="btnSelect"
        Text="Select"
        OnClick="btnSelect_Click"
        Runat="server" />
    <hr />
    <asp:Label
        id="lblSelectedProduct"
        Runat="server" />
    <asp:SqlDataSource
        id="srcProducts"
        SelectCommand="SELECT Id, Title FROM Products"
        ConnectionString="<%$ ConnectionStrings:Products %>"
        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></source>
    
   

== Enabling Automatic PostBacks==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<script runat="server">
    protected void ddlProducts_SelectedIndexChanged(object sender, EventArgs e)
    {
        lblSelectedProduct.Text = ddlProducts.SelectedItem.Text;
    }
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>AutoPostBack List Control</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:DropDownList
        id="ddlProducts"
        DataSourceID="srcProducts"
        DataTextField="Title"
        DataValueField="Id"
        AutoPostBack="true"
        OnSelectedIndexChanged="ddlProducts_SelectedIndexChanged"
        Runat="server" />
    <br /><br />
    <asp:Label
        id="lblSelectedProduct"
        Runat="server" />
    <asp:SqlDataSource
        id="srcProducts"
        SelectCommand="SELECT Id, Title FROM Products"
        ConnectionString="<%$ ConnectionStrings:Products %>"
        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></source>
    
   

== Link DropDownList with SqlDataSource and do the editing==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" AutoEventWireup="true"%>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Record Editor</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="lstProduct" 
                          runat="server" 
                          AutoPostBack="True" 
                          Width="280px" 
                          DataSourceID="sourceProducts" 
                          DataTextField="ProductName" 
                          DataValueField="ProductID">
        </asp:DropDownList>
        <br />
        <table>
            <tr>
                <td>
                    <asp:DetailsView ID="DetailsView1" 
                                     runat="server" 
                                     DataSourceID="sourceProductDetails"
                                     Height="50px" 
                                     Width="200px" 
                                     AutoGenerateEditButton="True">
                    </asp:DetailsView>
                </td>
                <td style="width: 190px">
                </td>
            </tr>
        </table>
        <asp:SqlDataSource ID="sourceProducts" 
                           runat="server"
                           ProviderName="System.Data.SqlClient"
                           ConnectionString="<%$ ConnectionStrings:Northwind %>"
                           SelectCommand="SELECT ProductName, ProductID FROM Products"/>
        <asp:SqlDataSource ID="sourceProductDetails" 
                           runat="server"
                           ProviderName="System.Data.SqlClient"
                           ConnectionString="<%$ ConnectionStrings:Northwind %>"
                           SelectCommand="SELECT ProductID, ProductName, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued FROM Products WHERE ProductID=@ProductID"
                           UpdateCommand="UPDATE Products SET ProductName=@ProductName, UnitPrice=CONVERT(money, @UnitPrice), UnitsInStock=@UnitsInStock, UnitsOnOrder=@UnitsOnOrder, ReorderLevel=@ReorderLevel, Discontinued=@Discontinued WHERE ProductID=@ProductID">
           <SelectParameters>
               <asp:ControlParameter ControlID="lstProduct" Name="ProductID" PropertyName="SelectedValue" />
           </SelectParameters>
        </asp:SqlDataSource>
        <asp:Label ID="lblInfo" runat="server" EnableViewState="False" Font-Bold="True" ForeColor="#C00000"></asp:Label>
        <hr />
</div>
    </form>
</body>
</html>

File: Web.config
<?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="Northwind" connectionString="Data Source=localhost\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI"/>
  </connectionStrings>
</configuration></source>
    
   

== Master/Details form with a list control==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<body>
    <form id="form1" runat="server">
    <div>
    <asp:DropDownList
        id="ddlProductCategory"
        DataSourceID="srcProductCategories"
        DataTextField="Name"
        DataValueField="Id"
        Runat="server" />
    <asp:Button
        id="btnSelect"
        Text="Select"
        Runat="server" />
    <asp:GridView
        id="grdProducts"
        DataSourceID="srcProducts"
        CssClass="gridView"
        Runat="server" />
    <asp:SqlDataSource
        id="srcProductCategories"
        SelectCommand="SELECT Id, Name FROM ProductCategories"
        ConnectionString="<%$ ConnectionStrings:Products %>"
        Runat="server" />
    <asp:SqlDataSource
        id="srcProducts"
        SelectCommand="SELECT Title,Director FROM Products
            WHERE CategoryId=@Id"
        ConnectionString="<%$ ConnectionStrings:Products %>"
        Runat="server">
        <SelectParameters>
        <asp:ControlParameter
            Name="Id"
            ControlID="ddlProductCategory"
            PropertyName="SelectedValue" />
        </SelectParameters>
    </asp:SqlDataSource>
    </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></source>
    
   

== Prevent overlapping edits.==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="MyPage" %>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Record Editor</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="lstProduct" 
                          runat="server" 
                          AutoPostBack="True" 
                          Width="300px" 
                          DataSourceID="sourceProducts" 
                          DataTextField="ProductName" 
                          DataValueField="ProductID">
        </asp:DropDownList>
        <br />
        <table>
            <tr>
                <td>
                    <asp:DetailsView ID="DetailsView1" 
                                     runat="server" 
                                     DataSourceID="sourceProductDetails"
                                     Height="50px" 
                                     Width="200px" 
                                     AutoGenerateEditButton="True">
                    </asp:DetailsView>
                </td>
                <td style="width: 190px">
                </td>
            </tr>
        </table>
        <asp:SqlDataSource ID="sourceProducts" 
                           runat="server"
                           ProviderName="System.Data.SqlClient"
                           ConnectionString="<%$ ConnectionStrings:Northwind %>"
                           SelectCommand="SELECT ProductName, ProductID FROM Products"/>
         <asp:SqlDataSource ID="sourceProductDetails" 
                            runat="server"
                            ProviderName="System.Data.SqlClient"
                            ConnectionString="<%$ ConnectionStrings:Northwind %>"
                            SelectCommand="SELECT ProductID, ProductName, UnitPrice, UnitsInStock, UnitsOnOrder, ReorderLevel, Discontinued FROM Products WHERE ProductID=@ProductID"
                            UpdateCommand="UPDATE Products SET ProductName=@ProductName, UnitPrice=@UnitPrice, UnitsInStock=@UnitsInStock, UnitsOnOrder=@UnitsOnOrder, ReorderLevel=@ReorderLevel, Discontinued=@Discontinued WHERE ProductID=@ProductID AND ProductName=@original_ProductName AND UnitPrice=@original_UnitPrice AND UnitsInStock=@original_UnitsInStock AND UnitsOnOrder=@original_UnitsOnOrder AND ReorderLevel=@original_ReorderLevel AND Discontinued=@original_Discontinued"
                            OldValuesParameterFormatString="original_{0}" ConflictDetection="CompareAllValues" OnUpdated="sourceProductDetails_Updated">
           <SelectParameters>
              <asp:ControlParameter ControlID="lstProduct" Name="ProductID" PropertyName="SelectedValue" />
           </SelectParameters>
        </asp:SqlDataSource>
        <asp:Label ID="lblInfo" runat="server" EnableViewState="False"></asp:Label>
    </div>
    </form>
</body>
</html>
File: Default.aspx.cs
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;
public partial class MyPage : System.Web.UI.Page
{
    protected void sourceProductDetails_Updated(object sender, SqlDataSourceStatusEventArgs e)
    {
        if (e.AffectedRows == 0)
        {
            lblInfo.Text = "No update was performed. A concurrency error is likely, or the command is incorrectly written.";
        }
        else
        {
            lblInfo.Text = "Record successfully updated.";
        }
    }
}

File: Web.config

<?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="Northwind" connectionString="Data Source=localhost\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI"/>
  </connectionStrings>
</configuration></source>
    
   

== Repeater and DropDownList==



   
  <!-- start source code -->
   
    <source lang="csharp">
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" 
    Inherits="Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Repeater in action</title>
</head>
<body>
    <div id="pageContent">
        <form id="form1" runat="server">
            <asp:DropDownList ID="Countries" runat="server" 
                AutoPostBack="true" 
                AppendDataBoundItems="True" 
                OnSelectedIndexChanged="Countries_SelectedIndexChanged">
                <asp:ListItem>[No country]</asp:ListItem>
            </asp:DropDownList>
            
            <asp:Repeater ID="Repeater1" runat="server">
                <HeaderTemplate>
                    <h2>We have customers in the following cities</h2>
                    <hr />
                </HeaderTemplate> 
                <SeparatorTemplate>
                    <hr noshade style="border:dashed 1px blue" />
                </SeparatorTemplate>
                <ItemTemplate>
                    <%# Eval("City") %> &nbsp;&nbsp;<b><%# Eval("Country")%></b>
                </ItemTemplate>
                <FooterTemplate>
                    <hr />
                    <%# CalcTotal() %> cities
                </FooterTemplate>
            </asp:Repeater>
        </form>
    </div>
</body>
</html>
File: Default.aspx.cs
using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default : System.Web.UI.Page
{
    DataTable data;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillCountries();
        }
    }
    protected void FillCountries()
    {
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
        string cmdText = "SELECT DISTINCT country FROM customers;";
        data = new DataTable();
        SqlDataAdapter adapter = new SqlDataAdapter(cmdText, connString);
        adapter.Fill(data);
        Countries.DataSource = data;
        Countries.DataTextField = "country";
        Countries.DataBind();
    }
    protected int CalcTotal()
    {
        return data.Rows.Count;
    }
    protected void Countries_SelectedIndexChanged(object sender, EventArgs e)
    {
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString;
        string cmdText = "SELECT DISTINCT country, city FROM customers WHERE country=@TheCountry";
        data = new DataTable();
        SqlDataAdapter adapter = new SqlDataAdapter(cmdText, connString);
        adapter.SelectCommand.Parameters.AddWithValue("@TheCountry", Countries.SelectedValue);
        adapter.Fill(data);
        Repeater1.DataSource = data;
        Repeater1.DataBind();
    }
}</source>
    
   

== Table record editor by DropDownList and ListBox==



   
  <!-- start source code -->
   
    <source lang="csharp">
File: index.aspx
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="RecordEditor" %>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Record Editor</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:DropDownList ID="lstProduct" 
                          runat="server" 
                          AutoPostBack="True" 
                          Width="280px" 
                          OnSelectedIndexChanged="lstProduct_SelectedIndexChanged">
        </asp:DropDownList>
        <table>
            <tr>
                <td>
                    <asp:Label ID="lblRecordInfo" runat="server"></asp:Label></td>
                <td>
                <asp:Panel ID="pnlCategory" runat="server" Visible="False">
                    <asp:ListBox ID="lstCategory" 
                                 runat="server" 
                                 Height="120px" 
                                 Width="152px">
                    </asp:ListBox>
                    <asp:Button ID="cmdUpdate" 
                                runat="server" 
                                Text="Update" 
                                OnClick="cmdUpdate_Click" />
                </asp:Panel>
                </td>
            </tr>
        </table>
        </div>
    </form>
</body>
</html>

File: Default.aspx.cs
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 System.Web.Configuration;
using System.Data.SqlClient;
public partial class RecordEditor : System.Web.UI.Page
{
    private string connectionString = WebConfigurationManager.ConnectionStrings["Northwind"].ConnectionString;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            string selectSQL = "SELECT ProductName, ProductID FROM Products";
            SqlConnection con = new SqlConnection(connectionString);
            SqlCommand cmd = new SqlCommand(selectSQL, con);
            con.Open();
            lstProduct.DataSource = cmd.ExecuteReader();
            lstProduct.DataTextField = "ProductName";
            lstProduct.DataValueField = "ProductID";
            lstProduct.DataBind();
            con.Close();
            lstProduct.SelectedIndex = -1;
        }
    }
    protected void lstProduct_SelectedIndexChanged(object sender, EventArgs e)
    {
        string selectProduct = "SELECT ProductName, QuantityPerUnit, " +
         "CategoryName FROM Products INNER JOIN Categories ON " +
         "Categories.CategoryID=Products.CategoryID " +
         "WHERE ProductID=@ProductID";
        
        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmdProducts = new SqlCommand(selectProduct, con);
        cmdProducts.Parameters.AddWithValue("@ProductID", lstProduct.SelectedItem.Value);
        using (con)
        {
            con.Open();
            SqlDataReader reader = cmdProducts.ExecuteReader();
            reader.Read();
            lblRecordInfo.Text = "<b>Product:</b> " + reader["ProductName"] + "<br />";
            lblRecordInfo.Text += "<b>Quantity:</b> " + reader["QuantityPerUnit"] + "<br />";
            lblRecordInfo.Text += "<b>Category:</b> " + reader["CategoryName"];
            string matchCategory = reader["CategoryName"].ToString();
            reader.Close();
            string selectCategory = "SELECT CategoryName, CategoryID FROM Categories";
            SqlCommand cmdCategories = new SqlCommand(selectCategory, con);
            lstCategory.DataSource = cmdCategories.ExecuteReader();
            lstCategory.DataTextField = "CategoryName";
            lstCategory.DataValueField = "CategoryID";
            lstCategory.DataBind();
            lstCategory.Items.FindByText(matchCategory).Selected = true;
        }
        pnlCategory.Visible = true;
    }
    protected void cmdUpdate_Click(object sender, EventArgs e)
    {
        string updateCommand = "UPDATE Products SET CategoryID=@CategoryID WHERE ProductID=@ProductID";
        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand(updateCommand, con);
        cmd.Parameters.AddWithValue("@CategoryID", lstCategory.SelectedItem.Value);
        cmd.Parameters.AddWithValue("@ProductID", lstProduct.SelectedItem.Value);
        using (con)
        {
            con.Open();
            cmd.ExecuteNonQuery();
        }
    }
}
File: Web.config
<?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="Northwind" connectionString="Data Source=localhost\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI"/>
  </connectionStrings>
</configuration></source>