Forms Data Controls :: Update Dropdownlist With Detailview Control - Set Update Parameters?

I searched a lot of threads but still couldn't get my problem fixed. I have to update the "regform" table with two fields: session_ and session2. These two fields are inside the detailview edititem template which bounded to dropdown list drpsession1, drpsession2 separately. I wanted to pass the update parameters to the update sql UPDATE dbo.regform SET session_=@session_, session2=@session2 where id=@id

the @session_ is bounded to a drpsession1 and @session2 is bounded to drpsession2. I used
ControlID="ctl00$ContentPlaceHolder1$DetailsView1$drpsession1" to access the dropdown list within the detailview, but still couldn't do the updates. What's wrong with my code? Do I have to use the code behind to specify the update parameters? and How to do it? TIA.

<
"
asp:DetailsView
ID="DetailsView1"
runat="server"
AutoGenerateRows="False"
DataSourceID="SqlDataSource2"
Height="50px"
Width="544px"
DataKeyNames="id"
ondatabound="DetailsView1_DataBound">
<Fields>
<
asp:TemplateField
HeaderText="Session -Part I"
SortExpression="session_">
<
EditItemTemplate>
<asp:DropDownList
ID="drpsession1"
runat="server"
DataSourceID="SqlDataSource3"
DataTextField="session_time"
DataValueField="session_id"
SelectedValue='<%# Bind("session_") %>'
AppendDataBoundItems="True"
Width="229px">
<asp:ListItem
Text="Please select"
Value="-1"
/>
</asp:DropDownList>
<asp:SqlDataSource
ID="SqlDataSource3"
runat="server"
ConnectionString="<%&#36; ConnectionStrings:Connstr %>"
SelectCommand="SELECT dbo.sessions.* FROM dbo.sessions"></asp:SqlDataSource>
</EditItemTemplate>
<
asp:TemplateField
HeaderText="Session - Part II"
SortExpression="session2">
<EditItemTemplate>
<asp:DropDownList
ID="drpsession2"
runat="server"
DataSourceID="SqlDataSource4"
DataTextField="session_time"
DataValueField="session_id"
SelectedValue='<%# Bind("session2") %>'
AppendDataBoundItems="True"
Width="234px">
<asp:ListItem
Text="Please select"
Value="-1"
/>
</asp:DropDownList>
<asp:SqlDataSource
ID="SqlDataSource4"
runat="server"
ConnectionString="<%&#36; ConnectionStrings:Connstr %>"
SelectCommand="SELECT dbo.sessions2.* FROM dbo.sessions2">
</asp:SqlDataSource>
</EditItemTemplate>
</Fields>
</asp:DetailsView>
<
asp:SqlDataSource
ID="SqlDataSource2"
runat="server"
ConnectionString="<%&#36; ConnectionStrings:Connstr %>"
UpdateCommand
where regform.id=@id">
="UPDATE dbo.regform SET session_=@session_, session2=@session2 where id=@id">
<UpdateParameters>
<asp:ControlParameter
ControlID="ctl00$ContentPlaceHolder1$DetailsView1$drpsession1"
Name="session_"
PropertyName="SelectedValue"
Type="String"
/>
<asp:ControlParameter
ControlID="ctl00$ContentPlaceHolder1$DetailsView1$drpsession2"
Name="session2"
PropertyName="SelectedValue"
Type="String"
/>
<asp:ControlParameter
ControlID="DetailsView1"
Name="id"
PropertyName="SelectedValue"
/>
</UpdateParameters>
</asp:SqlDataSource>