private void AnswerSet_EditCommand(object source, DataGridCommandEventArgs e)
{
   this.MyDataGrid.EditItemIndex = e.Item.ItemIndex;
   this.MyDataGrid.DataSource = this._question.AnswerSet;
   this.MyDataGrid.DataBind();
}

private void AnswerSet_UpdateCommand(object source, DataGridCommandEventArgs e)
{
   TextBox displayOrder = (TextBox) e.Item.FindControl("DisplayOrder");
   TextBox answerText = (TextBox) e.Item.FindControl("Text");
   TextBox scoreValue = (TextBox) e.Item.FindControl("ScoreValue");

   // apply values to my object within the AnswerSet collection
   // ...

   // call the update
   base.DomainManager.UpdateObject(this._question);

   this.MyDataGrid.EditItemIndex = -1;
   this.MyDataGrid.DataSource = this._question.AnswerSet;
   this.MyDataGrid.DataBind();
}

public void OnUpdate(object source, DataListCommandEventArgs e)
      {
         /* Get the updated values from the form */
         int vehicleID = Convert.ToInt32(vehiclesDataList.DataKeys[e.Item.ItemIndex].ToString());

         /* check date given is valid otherwise use todays date */
         DateTime date;
         string dateString = DataValidation.ValidateDate(((TextBox)(e.Item.FindControl("txtDate"))).Text);
         if (dateString != null)
         {   
            date = Convert.ToDateTime(dateString);
         }
         else
         {
            date = DateTime.Now;
         }

         /* check price is valid otherwise set to 0 - maybe change this? */
         decimal price;
         string priceString = DataValidation.ValidatePrice(((TextBox) e.Item.FindControl("txtPrice")).Text);
         if(priceString != null)
         {
            price = Convert.ToDecimal(priceString);
         }
         else
         {
            price = 0;
         }
         
         /* Get the other fields */
         string manufacturer = ((TextBox) e.Item.FindControl("txtManufacturer")).Text;
         string model = ((TextBox) e.Item.FindControl("txtModel")).Text;
         string regNumber = ((TextBox) e.Item.FindControl("txtRegNumber")).Text;
         
         string stockNumber = ((TextBox) e.Item.FindControl("txtStockNumber")).Text;
         string orderNumber = ((TextBox) e.Item.FindControl("txtOrderNumber")).Text;
         bool cancelled = ((CheckBox) e.Item.FindControl("chkIsCancelled")).Checked;
         bool readyToInvoice = ((CheckBox) e.Item.FindControl("chkIsReadyToInvoice")).Checked;

         int driverID = Convert.ToInt32(((DropDownList) e.Item.FindControl("lstDriver")).SelectedValue);
         int transporterID = Convert.ToInt32(((DropDownList) e.Item.FindControl("lstTransporter")).SelectedValue);
         int version = Convert.ToInt32(((Label) e.Item.FindControl("version")).Text);

         /* Get the session */
         ISession session = SessionHandler.CurrentSession;
         
         /* Get the selected driver & transporter */
         Driver driver = DataAccessLayer.GetDriverByID(driverID, session);
         Transporter transporter = DataAccessLayer.GetTransporterByID(transporterID, session);
         
         Vehicle vehicle = new Vehicle();
         vehicle.ID = vehicleID;
         vehicle.Version = version;

         /* Update vehicle fields here */
         // chopped for brevity

         if(vehicle.IsCancelled)
         {
            /* Delete the vehicle */
            SessionHandler.DeleteObject(vehicle);
         }
         else
         {
            /* Update vehicle */
            SessionHandler.UpdateObject(vehicle);
         }

         /* Unset edit row */
         this.vehiclesDataList.EditItemIndex = -1;
         BindGrid();
      }

another object with the same id was already associated with the session: [Vehicle#11]