TBufDataset+TDBGrid basic application problem (new records disappear)
lazarus / 16-Databases

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e5431 · 2026-03-20 20:07

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

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olatov · 2026-03-20 23:06

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?

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wp · 2026-03-21 00:36

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);begin 
BufDataset1.FieldDefs.Add('Name', ftString, 100); 
Bufdataset1.IndexDefs.Add('ASCENDING_ORDER', 'Name', []); 
Bufdataset1.IndexDefs.Add('DESCENDING_ORDER', 'Name',
[ixDescending]);  BufDataset1.IndexName := 'DESCENDING_ORDER'; 
BufDataset1.CreateDataset;  BufDataset1.Open; 
DBGrid1.Columns[0].Width := 100;end; This modification is running
fine.

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e5431 · 2026-03-21 03:19

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

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valdir.marcos · 2026-03-21 03:48

Quote from: wp on March 21, 2026, 01:36:04 amRunning 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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);begin 
BufDataset1.FieldDefs.Add('Name', ftString, 100); 
Bufdataset1.IndexDefs.Add('ASCENDING_ORDER', 'Name', []); 
Bufdataset1.IndexDefs.Add('DESCENDING_ORDER', 'Name',
[ixDescending]);  BufDataset1.IndexName := 'DESCENDING_ORDER'; 
BufDataset1.CreateDataset;  BufDataset1.Open; 
DBGrid1.Columns[0].Width := 100;end; This modification is running
fine.
Interesting.