Forms Data Controls :: Using The Selected Index Of A Gridview Where The Key Includes UserID?

I have Gridview1 that brings up the columns Resorts, Seasons, Seasons_ID, Resorts_ID, and User_ID

The three ID's are all foreign keys from related tables, and they are together a combined primary key of the table being accessed (they were defined that way to prevent duplicate entries for any User/Resort/Season combination).

Now the problem: I want to use the selected row from that gridview in the WHERE clause of a SQLDatasource by setting the WHERE clause up like:

WHERE (([Resort_ID] = @Resort_ID) AND ([Season_ID] = @Season_ID) AND ([User_ID] = @User_ID)) , with the parameters each coming from statements like

Gridview1.SelectedValue

When I select a row in the Gridview, I get the following error:

Operand type clash: uniqueidentifier is incompatible with int

I am pretty sure this has to do with the User_ID being in the WHERE clause.

So I have tried something like this to access the selected index:

Gridview1.DataKeys(Gridview1.SelectedIndex).Value

This does not work, as it seems to return only the first key (of three) in the DataKeyNames list.

So the question: How can I use the SelectedIndex of that gridview for such a purpose when the key contains a UserID?