Update e Delete com DBGrid

Caros Colegas

Ao tentar executar um delete ou update através de um dbgrid o processo nao esta sendo gravado no banco, segue abaixo o exemplo utilizado

desde ja agradeço
att
EMERSON

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, DBCtrls, DB, IBCustomDataSet, IBDatabase, Grids,
DBGrids;

type
TForm1 = class(TForm)
DBGrid1: TDBGrid;
IBDatabase1: TIBDatabase;
DataSource1: TDataSource;
IBDataSet1: TIBDataSet;
IBTransaction1: TIBTransaction;
IBDataSet1CODIGO: TIntegerField;
IBDataSet1DESCRICAO: TIBStringField;
IBDataSet1VALOR_COMPRA: TFloatField;
DBNavigator1: TDBNavigator;
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

end.