string InsertOrUpdateQueryStringItem(string key, string value)

         {

             if (Request.QueryString.HasKeys())

             {

                 if (!Array.Exists<string>(Request.QueryString.AllKeys, (qs) => { return qs.Equals(key); }))

                 {

                     return string.Format("{0}&{1}={2}", Request.RawUrl, key, value);

                 }

                 else

                 {

                     System.Text.StringBuilder pathBuilder = new System.Text.StringBuilder(Request.Path);

                     pathBuilder.Append("?");

                     string keyValue;

                     string keyCurrent;

                     int handedCount = ;

                     foreach (var k in Request.QueryString.AllKeys)

                     {

                         if (!k.Equals(key))

                         {

                             keyValue = Request.QueryString[k];

                             keyCurrent = k;

                         }

                         else

                         {

                             keyValue = value;

                             keyCurrent = key;

                         }

                         if (string.IsNullOrEmpty(keyValue))

                         {

                             continue;

                         }

                         if (handedCount++ != )

                         {

                             pathBuilder.AppendFormat("&{0}={1}", keyCurrent, keyValue);

                         }

                         else

                         {

                             pathBuilder.AppendFormat("{0}={1}", keyCurrent, keyValue);

                         }

                     }

                     return pathBuilder.ToString();

                 }

             }

             return string.Format("{0}?{1}={2}", Request.Path, key, value);

         }