MxBtbase.BtRecordset rs = new MxBtbase.BtRecordset();
rs.BtDatabase = db;
string rok = connection.FirmaInfo.get_Rok(connection.FirmaInfo.OstatniRok).Katalog;

rs.Open("kursy", rok + "\\01KURSY.DAT");
rs.SetKey("symbol");
rs.set_KeyField("symbol", wartoscWaluty.symbol);
rs.set_KeyField("data", wartoscWaluty.date.ToShortDateString());

short error = rs.GetRec(MxBtbase.BO.GETEQ);

if (string.IsNullOrEmpty(rs["waluta1"]))
{
       rs["data"] = wartoscWaluty.date.ToShortDateString();
       rs["symbol"] = wartoscWaluty.symbol;
       rs["waluta1"] = wartoscWaluty.waluta;               
       rs["zakup1"] = wartoscWaluty.zakup;
       rs["sprz1"] = wartoscWaluty.sprzedaz;
}
rs.Insert();
rs.Close();

       rs["zakup1"] = 4.1234;
       rs["sprz1"] = 4,1234;

       rs.Value["zakup1"] = 4.1234;
       rs.Value["sprz1"] = 4,1234;

rs["zakup1"] = 4.1234;
rs["zakup1"] = "4,1234";
rs["zakup1"] = "4.1234";