Delphi Community database tutorials, part 3
Saving to / loading from a disk file

Let's add some code for saving the database to a file.

1. In the source editor, under Private declarations, add the following lines:
   

   private
     { Private declarations}
     XmlFile: string;
     DataChanged: Boolean;

2. In the implementation section, modify procedure TForm1.FormCreate as follows:
   

   procedure TForm1.FormCreate(Sender: TObject);
   begin
     DataChanged := False;
     XmlFile := 'ufodata.xml';
     if FileExists(XmlFile) then
       cdsUfo.LoadFromFile(XmlFile)
     else begin
       cdsUfo.FieldDefs.Add('ID',       ftString, 10, False);
       cdsUfo.FieldDefs.Add('DESC',     ftString, 25, False);
       cdsUfo.FieldDefs.Add('LOCATION', ftString, 16, False);
       cdsUfo.FieldDefs.Add('COUNTRY',  ftString, 16, False);
       cdsUfo.FieldDefs.Add('CE',       ftString,  1, False);
       cdsUfo.FieldDefs.Add('SOURCE',   ftString, 25, False);
       cdsUfo.FieldDefs.Add('DURAT',    ftString, 16, False);
       cdsUfo.FieldDefs.Add('WIT',      ftString,  5, False);
       cdsUfo.FieldDefs.Add('SHAPE',    ftString, 10, False);
       cdsUfo.FieldDefs.Add('APPEAR',   ftString, 10, False);
       cdsUfo.FieldDefs.Add('SIZE',     ftString, 10, False);
       cdsUfo.FieldDefs.Add('OCC',      ftString,  3, False);
       cdsUfo.FieldDefs.Add('LINK2',    ftString, 50, False);
       cdsUfo.FieldDefs.Add('NOTES',    ftMemo,   10, False);
       cdsUfo.CreateDataSet;
       DataChanged := True;
     end;
     cdsUfo.LogChanges := False;
   end;

3. Select cdsUfo. In the Object Inspector, tab Events, double click next to AfterDelete.
   In the Code Editor, complete the newly created event handler as follows:
   

   procedure TForm1.cdsUfoAfterDelete(DataSet: TDataSet);
   begin
     DataChanged := True;
   end;

4. In the Object Inspector, create an OnClose event handler for Form1.
   In the Code Editor, complete the event handler as follows:
   

   procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
   begin
     if DataChanged then
       cdsUfo.SaveToFile(XmlFile, dfXML);
   end;

5. Run your program (press F9). Add, modify and delete a few records.
6. Stop the program.

Database Tutorials - Part 2    Database Tutorials - Part 4