//以前我写过一个测试的，是没问题的，返回是值的长度而已
        protected long GetLength(int id)
        {
            OracleConnection conn = null;
            OracleCommand cmd = null;
            OracleDataReader dr = null;
            string sConn = "data source=orcl;user id=zhangandli;password=1;";
            try
            {
                conn = new OracleConnection(sConn);
                cmd = new OracleCommand("select b from t where id=1", conn);
                conn.Open();
                dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                if (dr.Read())
                {
                    if (dr[0].ToString() != "")
                    {
                        byte[] blob = (byte[])dr[0];
                        return blob.Length;
                    }
                }
            }
            catch
            {
                return 0;
            }
            finally
            {
                dr.Close();
            }
            return 0;
        }