Wednesday, 12 September 2012

How to use SaveToFile and LoadFromFile in Delphi XE2?


The data retrieved via an ADO dataset component can be saved to a file for later retrieval on the same or a different computer. Save the data to a file using the SaveToFile method. Retrieve the data from file using the LoadFromFile method. The data is saved in one of two proprietary formats: ADTG and XML. Indicate which of these two formats to use for the save file with one of the TPersistFormat constants pfADTG or pfXML in the Format parameter of the SaveToFile method.

procedure TForm1.SaveBtnClick(Sender: TObject);
begin
  if (FileExists('c:\SaveFile')) then begin
    DeleteFile('c:\SaveFile');
    StatusBar1.Panels[0].Text := 'Save file deleted!';
  end;
  ADODataSet1.SaveToFile('c:\SaveFile', pfADTG);
end;

procedure TForm1.LoadBtnClick(Sender: TObject);
begin
  if (FileExists('c:\SaveFile')) then
    ADODataSet2.LoadFromFile('c:\SaveFile')
  else
    StatusBar1.Panels[0].Text := 'Save file does not exist!';
end;

Explanation: In the example above, the first procedure saves the dataset retrieved by the TADODataSet component ADODataSet1 to a file. The target file is an ADTG file named SaveFile, saved to a local drive. The second procedure loads this saved file into the TADODataSet component ADODataSet2.

The saving and loading dataset components need not be on the same form as above, in the same application, or even on the same computer. This allows for the briefcase-style transfer of data from one computer to another.

On calling the LoadFromFile method, the dataset component is automatically activated.

If the file specified in the FileName parameter of the SaveToFile method already exists, an EOleException exception is raised. Similarly, if the file specified in the FileName parameter of LoadFromFile does not exist, an EOleException exception is raised.

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