How to pass session variable as ContextKey in ASP.Net Ajax Autocomplete extender

I think this might help you just take a look

Code

 protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                AutoCompleteExtender1.ContextKey = "Cornwall";
            }
        }

        [System.Web.Script.Services.ScriptMethod()]
        [System.Web.Services.WebMethod()]
        public static List<string> GetEmployees(string prefixText, int count, string contextKey) 
        {
            string query = "SELECT EmployeeId,GivenName FROM Employees WHERE Surname LIKE '%"+prefixText + "%' AND City = '"+ contextKey +"'";
            DataTable newDataTable = AutoCompleteExtender.GetData(query);
            List<string> searchedList = new List<string>();
            foreach (DataRow item in newDataTable.Rows)
            {
                searchedList.Add(item.Field<int>("EmployeeId").ToString());
            }
            return searchedList;
        }

        private static DataTable GetData(string cmdText) {

            OdbcConnection cn = new OdbcConnection("Dsn=SQL Anywhere 12 Demo;uid=dba");
            OdbcDataAdapter da = new OdbcDataAdapter(cmdText,cn);
            DataTable dt = new DataTable();
            da.Fill(dt);
            return dt;
        }

Html

 <asp:ScriptManager ID="src" runat="server">
        </asp:ScriptManager>
        <asp:TextBox ID="txtSearchEmployee" runat="server"></asp:TextBox>
        <asp:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server" ServiceMethod="GetEmployees"
            CompletionSetCount="10" CompletionInterval="100" MinimumPrefixLength="2" UseContextKey="true"
            FirstRowSelected="false" TargetControlID="txtSearchEmployee">
        </asp:AutoCompleteExtender>