cascading dropdownlist in gridview edit mode

<asp:GridView runat="server" DataSourceID="GVProductDS"  ID="GVAvailability" DataKeyNames="incident_id"
            AutoGenerateColumns="False" AllowPaging="True" AllowSorting="True" OnRowDataBound="GVAvailability_RowDataBound" OnRowUpdating="GVAvailability_RowUpdating" >
            <Columns>
                <asp:CommandField ShowDeleteButton="True" ShowEditButton="True" />
                <asp:BoundField DataField="incident_id" HeaderText="incident_id" 
                    SortExpression="incident_id" InsertVisible="False" ReadOnly="True" />
                <asp:TemplateField HeaderText="product_code" SortExpression="product_code">
                    <EditItemTemplate>
                        <asp:DropDownList ID="DDLProductCode" runat="server" DataSourceID="DDLProductDS" AutoPostBack= "true"
                            DataTextField="product_code" DataValueField="product_code" OnSelectedIndexChanged="DDLProductCode_OnSelectedIndexChanged">
                        </asp:DropDownList>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="Label1" runat="server" Text='<%# Bind("product_code") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="platform_id" SortExpression="platform_id">
                    <EditItemTemplate>
                        <asp:DropDownList ID="DDLPlatform" runat="server" 
                            DataSourceID="DDLPlatformDS" DataTextField="platform_id" 
                            DataValueField="platform_id">
                        </asp:DropDownList>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="Label2" runat="server" Text='<%# Bind("platform_id") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="incident_type" SortExpression="incident_type">
                    <EditItemTemplate>
                        <asp:TextBox ID="TextBox3" runat="server" Text='<%# Bind("incident_type") %>'></asp:TextBox>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:Label ID="Label3" runat="server" Text='<%# Bind("incident_type") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
<asp:SqlDataSource 
ID="DDLProductDS" 
runat="server" 
ConnectionString="<%$ ConnectionStrings:EMPortalConnectionString %>"

SelectCommand="SELECT DISTINCT product_name, [00_sla_product].product_code as product_code FROM 
[00_stage_availability_platforms], [00_sla_product] 
WHERE [00_stage_availability_platforms].product_code = [00_sla_product].product_code 
and [00_stage_availability_platforms].product_code not in (81,86) 
UNION 
SELECT 'Crossroads' as product_name, '00' as product_code 
UNION 
SELECT 'SMS-IG / SMS-IP' as product_name, '81' as product_code 
ORDER BY product_name 
"> 
</asp:SqlDataSource>            
<asp:SqlDataSource ID="DDLPlatformDS" runat="server" 
            ConnectionString="<%$ ConnectionStrings:EMPortalConnectionString %>" SelectCommand="
SELECT platform_name, platform_id
FROM [00_stage_availability_platforms]
WHERE product_code = @product_code">
   <SelectParameters>           
                <asp:controlparameter Name="product_code" controlid="DDLProductCode" DefaultValue="03"  Type="String" propertyname="SelectedValue"/>
            </SelectParameters>
</asp:SqlDataSource>
<asp:SqlDataSource ID="DDLTypeDS" runat="server" 
            ConnectionString="<%$ ConnectionStrings:EMPortalConnectionString %>" 
            SelectCommand="SELECT type_descr, TYPE_ID from [00_stage_availability_types]">
</asp:SqlDataSource>
<asp:SqlDataSource ID="GVProductDS" runat="server"
            ConnectionString="<%$ ConnectionStrings:EMPortalConnectionString %>" DeleteCommand="DELETE FROM [EMPortal].[dbo].[00_stage_availability]
      WHERE incident_id=@incidentID" 
            SelectCommand="SELECT incident_id, [product_code], [platform_id], [incident_type] FROM [00_stage_availability]" 
            UpdateCommand="UPDATE [EMPortal].[dbo].[00_stage_availability]
   SET [product_code] = @product_code,
      ,[platform_id] = @platform_id,
      ,[incident_type] = @incident_type
 WHERE incident_id=@incidentID ">
 <UpdateParameters>
                <asp:Parameter Name="product_code" />
                <asp:Parameter Name="platform_id" />
                <asp:Parameter Name="incident_type" />
            </UpdateParameters>
 </asp:SqlDataSource>

public partial class ServiceAvailabilityMaintainence : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void GVAvailability_RowDataBound(object sender, GridViewRowEventArgs e)
    {


        if ((e.Row.RowState & DataControlRowState.Edit) == DataControlRowState.Edit)
        {
            DataRowView dv = (DataRowView)e.Row.DataItem;

            //// Preselect correct value in product list
            DropDownList DDLProductCode = (DropDownList)e.Row.FindControl("DDLProductCode");


            DDLProductCode.SelectedValue = dv["product_code"].ToString();

            // Databind list of platforms in dependent drop-down list
            DropDownList DDLPlatform = (DropDownList)e.Row.FindControl("DDLPlatform");
            SqlDataSource dsc = (SqlDataSource)e.Row.FindControl("DDLPlatformDS");
            if(dsc!=null)
            dsc.SelectParameters["product_code"].DefaultValue = dv["product_code"].ToString();

            DDLPlatform.DataBind();
            DDLPlatform.SelectedValue = (dv["platform_id"].ToString());

        }
    }
    protected void DDLProductCode_OnSelectedIndexChanged(object sender, EventArgs e)
    {
        DropDownList DDLProductCode;
        DropDownList DDLPlatform;
        SqlDataSource DDLPlatformDS;
        int currentRowInEdit = GVAvailability.EditIndex;
        DDLProductCode = (DropDownList)sender;
        DDLPlatform = (DropDownList)GVAvailability.Rows[currentRowInEdit].FindControl("DDLPlatform");
        DDLPlatformDS = (SqlDataSource)GVAvailability.Rows[currentRowInEdit].FindControl("DDLPlatformDS");
        DDLPlatformDS.SelectParameters["product_code"].DefaultValue = DDLProductCode.SelectedValue;
        DDLPlatform.DataBind();
    }

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