C# รบกวนสอบเกี่ยวกับการส่งค่า Session ด้วยค่ะ

        //string test = "";
        ArrayList facArrList = new ArrayList();
        foreach (ListItem facItem in cblFac.Items)
        {
            if (facItem.Selected)
            {
                //test += facItem.Value + ":" + facItem.Text + "/";
                facArrList.Add(facItem.Value);
            }
        }
        //lbTest.Text = test;
        Session["facId"] = facArrList.ToString();
        //Session["facId"] = "12";

<asp:SqlDataSource SelectCommand="SELECT *  FROM ... WHERE FAC_ID IN (:facID)">
        <SelectParameters>
            <asp:SessionParameter Name="facID" SessionField="facID"/>      
        </SelectParameters>
<asp:SqlDataSource