Unassigned Parameter in ODP.NET and System.Data.OracleClient

using (OracleConnection cn = new OracleConnection(

    "Data Source=MyOracle;User Id=myUser;Password=myPass;"))

{

    OracleCommand cmd = new OracleCommand(

        "SELECT * FROM UserTable WHERE UserId = :userId", cn);

    cmd.Parameters.Add("userId", OracleType.VarChar);

    OracleDataAdapter da = new OracleDataAdapter(cmd);

    DataTable dt = new DataTable();

    if (bMode == "Add")

    {

        da.Fill(dt);

        DataRow row = dt.NewRow();

        row["UserId"] = "AAA";

        row["UserName"] = "UserAAA";

        dt.Rows.Add(row);

        da.Update(dt);

    }

    else if (bMode == "Update")

    {

        //...略...

    }

}