Please help: TDbf.RecNo do not working properly
lazarus / 16-Databases

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Handoko · 2009-03-06 06:11

I'm using:
Lazarus 0.9.26 Beta i386-win32 SVN 16885
FPC 2.2.2
DBFLaz 0.1.1


Hi, I found a bug in unit dbf (DBFLaz package).

If you insert some record, delete it, and insert some new record
again. The data you read will not be correct. I have tried it several
times using different data, I'm sure it always happen. Packing the
table will solve the problem. And if you create a new table, insert
some record and read it (without any deletion previously), you will
get the correct data.

Strangely, TDBGrid will show the record correctly. I also try using
CDBF Explorer (a freeware dbf utility), the record show correctly. So
I think the problem only happend if I use coding to the manipulate the
data. What I suspect is RecNo := xxx do not working properly.

Here, I explain it simply:
- A bug in TDbf (unit dbf, DBFLaz package)
- Record read incorrectly if there is any deleted record previously
- Packing the table can solve the problem
- Problem happen if you use coding to manipulate the record
- Problem will not happen if you use a TDBGrid to show the data
- I suspect TDbf.RecNo := xxx do not working properly

Of course, I can pack the table each time before I use coding to
manipulate the data. But you know it is not a good solution. I've
report the bug at Lazarus Bug Tracker. Anybody here please help me. If
you experience same problem, post your comment at the Bug Tracker
forum ID no. 13285.

Here is a sample code: (uses unit dbf and db)

procedure TForm1.Button1Click(Sender: TObject);
var
  DbfTest: TDbf;
  Sum: Integer;
  Z: Integer;
begin

  DbfTest := TDbf.Create(nil);
  with DbfTest do begin
    FilePathFull := 'c:\';
    TableName := 'Test.dbf';
    FieldDefs.Add('QTY', ftInteger);
    CreateTable;
    Open;

    // Insert data, then delete it
    Insert; FieldByName('QTY').AsInteger := 20; Post;
    Delete;

    // Insert 20 and 15, so the summary should be 35
    Insert; FieldByName('QTY').AsInteger := 20; Post;
    Insert; FieldByName('QTY').AsInteger := 15; Post;

    // Start calculating
    Sum := 0;
    for Z := 1 to ExactRecordCount do begin
      RecNo := Z;
      Sum := Sum + FieldByName('QTY').AsInteger;
      end;

    // But the result do not as expected
    MessageDlg('Result', IntToStr(Sum), mtInformation, [mbOK], 0);

    Close;
    Free;
    end;

end;

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DougNettleton · 2009-03-06 16:22

I'm not sure I would call it a bug.

You've got 3 records on your file.  The first one is deleted.  Your
code says basically:

goto record 1, add qty to summary
goto record 2, add qty to summary

and because you've deleted record 1 you expect it to read records 2
and 3.  Let's say you had 10 records and you deleted 2,4,6,8, and 10,
would expect your code to read records 1,3,5,7, and 9?  And what would
you expect if "ShowDeleted" was set to true?

try:

    Sum := 0;
    Dbf1.First;
    while not Dbf1.EOF do
    begin
      Sum := Sum + FieldByName('QTY').AsInteger;
      Dbf1.Next;
    end;

HTH,

Doug