Нow to dynamically change query for ListView linked to LinqDataSource?

In order to dynamically change query for ListView linked to LinqDataSource you have to handle OnSelecting event for LinqDataSource. .

For example:

      protected void dsMates_Selecting(object sender, LinqDataSourceSelectEventArgs e)
      {
          if (Request.Params["classMateId"] != null)
          {
              int mateId;
              if (int.TryParse(Request.Params["classMateId"], out mateId))
              {
                  using (DataClassesPrivateMsgDataContext db = new DataClassesPrivateMsgDataContext())
                  {
                      e.Result = db.Classmates.Where(mate => mate.Id == mateId).FirstOrDefault();
                  }
              }
          }
      }

How does it works you can see here: 11-A