Programmatisk datalæsning

Hej,
jeg har et gridview, hvor man kan select en bog, hvornæst info om forfatteren skal blive vist i et detailsview..

Det udkommenterede, '//GridView1.DataKeyNames = "BookID";', er det der giver problemer. Får fejlen "cannot implicitly convert type 'string' to 'string[]'" .. Men det er DataKeyNames jeg mangler at angive ikke? Og hvorn gør jeg så det :) ?

{
        GridView1.AutoGenerateSelectButton = true;

        string connectionString = WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection myConnection = new SqlConnection(connectionString);
        SqlCommand myCommand = new SqlCommand("Select * from Book", myConnection);
        SqlDataAdapter adapter = new SqlDataAdapter(myCommand);
        DataSet ds = new DataSet();

        try
        {
            myConnection.Open();
            adapter.Fill(ds, "Books");
        }
        catch (Exception err)
        {
            Response.Write(err);
        }
        finally
        {
            myConnection.Close();
        }
        GridView1.DataSource = ds.Tables["Books"];
        //GridView1.DataKeyNames = "BookID";
        GridView1.DataBind();       
    }
    protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string connectionString = WebConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
        SqlConnection myConnection = new SqlConnection(connectionString);
        SqlCommand myCommand = new SqlCommand("Select * from Person where PersonID = @AuthorID", myConnection);
        SqlDataAdapter adapter = new SqlDataAdapter(myCommand);
        DataSet ds = new DataSet();

        myCommand.Parameters.Add("@AuthorID", SqlDbType.Int);
        myCommand.Parameters["@AuthorID"].Value = GridView1.SelectedValue;
       

        try
        {
            myConnection.Open();
            adapter.Fill(ds, "Authors");
        }
        catch (Exception err)
        {
            Response.Write(err);
        }
        finally
        {
            myConnection.Close();
        }
        DetailsView1.DataSource = ds.Tables["Authors"];
        DetailsView1.DataBind();
    }