Sorting in Gridview Control

Write the following code In .aspx page :

<asp:GridView ID="gvstudents" runat="server" AllowSorting="true" 

    OnSorting="gvstudents_sorting">

    </asp:GridView>

Code in .aspx.cs:

public partial class SortingEx : System.Web.UI.Page

{

    

    protected void Page_Load(object sender, EventArgs e)

    {

        if(!IsPostBack)

        {

            string strcon = "data source=name of sql server ;initial catalog=database name;integrated security=sspi or user id=sqlserver userid ; password=somepassword";

            string sConnection = strcon;

            DataSet ds = new DataSet();

            SqlConnection cn = new SqlConnection(sConnection);

            using (cn)

            {

                SqlCommand cmd = new SqlCommand("select * from employees", cn);

                using (cmd)

                {

                    SqlDataAdapter da = new SqlDataAdapter();

                    da.SelectCommand = cmd;

                    da.Fill(ds);

                    gvstudents.DataSource = ds;

                    gvstudents.DataBind();

                    Session["ds"] = ds;

                    ViewState["sortcolumn"] = string.Empty;

                    ViewState["sortdirection"] = string.Empty;

                }

            }

        }

    }

    protected void gvstudents_sorting(object sender, GridViewSortEventArgs e)

    {

        if (Session["ds"] != null)

        {

           DataSet ds = (DataSet)Session["ds"];

           DataTable dt = ds.Tables[0];

           DataView dv = dt.DefaultView;//DataView ado.net view in t-sql 

            if (ViewState["sortcolumn"].ToString() == e.SortExpression.ToString())

            {

                if ("asc" == ViewState["sortdirection"].ToString())

                {

                    ViewState["sortdirection"] = "DESC";

                }

                else

                {

                    ViewState["sortdirection"] = "asc";

                }

            }

            else

            {

                ViewState["sortcolumn"] = e.SortExpression.ToString();

                ViewState["sortdirection"] = "asc";

            }

            if (dv != null)

            {

                dv.Sort = e.SortExpression + " " + ViewState["sortdirection"].ToString();

                //dv.Sort= "ename asc";

                gvstudents.DataSource = dv;

                gvstudents.DataBind();

            }

        }

    }

}

Table structure :

eid	fname	lname	age	salary	dept	doj
1	rajeev	sukla	23	12000	.net	23-Oct-11 12:00:00 AM
2	sowmya	kumari	23	19000	db	13-Nov-10 12:00:00 AM
3	kishore	kumar	27	36000	android	16-Oct-11 12:00:00 AM
4	abimanyu	biswal	22	null	android	20-Feb-10 12:00:00 AM
5	soni	kumar	24	21800	.net	21-Jun-09 12:00:00 AM
6	anu	_singh	22	12000	db	23-Oct-10 12:00:00 AM
7	_dinesh	moh%anty	23	15000	.net	26-Aug-09 12:00:00 AM
8	nishala	_kumari	22	18000	db	19-Jul-08 12:00:00 AM
1	rajeev	sukla	23	12000	.net	23-Oct-11 12:00:00 AM