You access individual records in a TDataSet using its Fields property or its FieldByName method. Fields is a collection property, and you must pass it an index that identifies which field you want to read from or write to, based on its zero-based ordinal position in the table's structure. When you invoke FieldByName, you pass a string containing the name of the field you want to work with. This approach works for any AdsTable, AdsQuery, or AdsStoredProc component that returns a result set.

The following event handler, associated with the Get Address button (shown in Figure 15-2), demonstrates how to read a field:

procedureC TForm1.GetAddressBtnClick(Sender: TObject);
begin
 if AdsTable1.Active then AdsTable1.Close;
 AdsTable1.TableName := 'CUSTOMER';
 AdsTable1.IndexName := 'Customer ID';
 AdsTable1.Open;
 if AdsTable1.FindKey([CustNoText.Text]) then
   OldAddressText.Text :=
     AdsTable1.FieldByName('Address').AsString
 else
   ShowMessage('Customer ID ' + CustNoText.Text +
     ' not found');
 DataSource1.DataSet := AdsTable1;
end;

The following event handler, associated with the Set New Address button (shown in Figure 15-2), demonstrates writing to a field:

procedure TForm1.SetAddressBtnClick(Sender: TObject);
begin
 if AdsTable1.Active then AdsTable1.Close;
 AdsTable1.TableName := 'CUSTOMER';
 AdsTable1.IndexName := 'Customer ID';
 AdsTable1.Open;
 if AdsTable1.FindKey([CustNoText.Text]) then
 begin
   AdsTable1.Edit;
   AdsTable1.FieldByName('Address').AsString :=
     NewAddressText.Text;
   AdsTable1.Post;
 end
 else
   ShowMessage('Customer ID ' + CustNoText.Text +
     ' not found');
 DataSource1.DataSet := AdsTable1;
end;