TBufDataset+TDBGrid basic application problem (new records disappear)

[e5431]

Hi everyone!
I'm trying to make a simple BufDataset application for storing a name list in a BufDataset in Lazarus 4.2+FPC 3.2.2 on Win 10 x64.
I put  TBufDataset, TDataSource, TDBGrid and TDBNavigator on my form with DataSet and DataSource properties filled.
When I run the application and click Insert button and type in a name, press Enter and then click Post, the name disappears from the grid (I've attached a gif for illustration).
If I keep adding new records, the new ones disappear after Post as well.
But sometimes some of them appear in the grid again.

When closing the application I get
'External: ACCESS VIOLATION' with message
Access violation reading from address $FFFFFFFFFFFFFFFF.

I can't understand what I do wrong. There is no code at all!
I recall when I wrote a similar app in Dephi 7, it worked fine.

Please help me to fix the issue.

PS: the archive with Lazarus project attached

[Nimbus]

Hi, I've tried your project (built using Lazarus 4.6 / FPC trunk under Linux) and it seems to be fine, can't see any problem.
Insert, edit, delete, post all work as expected.
Perhaps something's up with specific FPC/Laz version?

[wp]

Running your demo on Laz/main+FPC3.2.2 (32-bit) on Windows 11 I do get the same issue: only empty cells in the grid.

Your code contains persistent fields and designtime-created index defs. I am aware that that Lazarus/FPC are doing a bad job with databases at designtime. Maybe this has improved with FPC-trunkl because Nimbus does not see this issue (TBufDataset resides in FPC, not in Lazarus).

Usually it helps to avoid designtime operations with databases and do everything at runtime. I deleted the persistent field and the indexdefs - and suffered from some Lazarus crashes along the way. The better way probably is to delete the BufDataset altogether and just add a default one again. Then, use the OnCreate handler of the form to define the fields and indexes by code:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. begin
3.   BufDataset1.FieldDefs.Add('Name', ftString, 100);
4.   Bufdataset1.IndexDefs.Add('ASCENDING_ORDER', 'Name', []);
5.   Bufdataset1.IndexDefs.Add('DESCENDING_ORDER', 'Name', [ixDescending]);
6.   BufDataset1.IndexName := 'DESCENDING_ORDER';
7.   BufDataset1.CreateDataset;
8.   BufDataset1.Open;
9.   DBGrid1.Columns[0].Width := 100;
10. end;

This modification is running fine.

[e5431]

wp: Thank you! It really works.
I hope it will be possible someday to do the things in design time without problems.

[valdir.marcos]

Running your demo on Laz/main+FPC3.2.2 (32-bit) on Windows 11 I do get the same issue: only empty cells in the grid.

Your code contains persistent fields and designtime-created index defs. I am aware that that Lazarus/FPC are doing a bad job with databases at designtime. Maybe this has improved with FPC-trunkl because Nimbus does not see this issue (TBufDataset resides in FPC, not in Lazarus).

Usually it helps to avoid designtime operations with databases and do everything at runtime. I deleted the persistent field and the indexdefs - and suffered from some Lazarus crashes along the way. The better way probably is to delete the BufDataset altogether and just add a default one again. Then, use the OnCreate handler of the form to define the fields and indexes by code:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. begin
3.   BufDataset1.FieldDefs.Add('Name', ftString, 100);
4.   Bufdataset1.IndexDefs.Add('ASCENDING_ORDER', 'Name', []);
5.   Bufdataset1.IndexDefs.Add('DESCENDING_ORDER', 'Name', [ixDescending]);
6.   BufDataset1.IndexName := 'DESCENDING_ORDER';
7.   BufDataset1.CreateDataset;
8.   BufDataset1.Open;
9.   DBGrid1.Columns[0].Width := 100;
10. end;

This modification is running fine.

Interesting.