Untraceable access violation when opening a sqlite db the 2nd time
lazarus / 16-Databases

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dietmar · 2021-09-29 18:15

Hi,

I am using this code to open a sqlite DB:
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 function
TDBHelper.OpenDB(fn: String): Boolean;var s: String;begin   
SQLite3Connection.DatabaseName := fn;    try     
SQLite3Connection.Open;      if SQLite3Connection.Connected then     
begin        SQLTransaction.Active := True;      end... 
Then I am executing SELECT statements on it which works fine.

Then, after closing the DB via SQLite3Connection.Close; I am running
into access violations when I try to (re)open the database.

What am I doing wrong?

Thx,
--Dietmar

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MarkMLl · 2021-09-29 19:43

Quote from: dietmar on September 29, 2021, 08:15:59 pmWhat am I doing
wrong?

Not attaching a complete program that people can use to duplicate your
problem.

MarkMLl

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marcov · 2021-09-29 20:05

I never used sqllite with transaction, but maybe close transaction
first ?

Maybe the transaction component is left in some indefinite state.

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dietmar · 2021-09-30 13:07

Attached is my small test project, but unfortunately, that even throws
an error before the "interesting part": Access violation reading... in
line 46 of tdbhelper. Don't know, what's going wrong here, it works in
my main program.

If it runs, you should be able to reproduce the error by "open" ->
"close" -> "open" buttons...

--Dietmar

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balazsszekely · 2021-09-30 15:14

Hi dietmar,

QuoteAttached is my small test project, but unfortunately, that even
throws an error before the "interesting part": Access violation
reading... in line 46 of tdbhelper. Don't know, what's going wrong
here, it works in my main program.

Form DBHelper is nil. You have to choices:
    1. Add DBHelper to the auto-create forms(project options)
    2. Create the form before calling method OpenDB:
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    dbHelper
:= TdbHelper.Create(Application);  //this line  if
(DBHelper.OpenDB(ExtractFilePath(Application.Location) + 'test.db'))
then begin    Query := TSQLQuery.Create(nil);    try      Query :=
DBHelper.SelectQuery('SELECT * FROM Owner LIMIT 1;');     
StaticText1.Caption := Query.FieldByName('Wiz_Name').AsString;   
finally      Query.Free;    end;  end;

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dietmar · 2021-09-30 16:25

Ok, after adding the form the the loadings, one can start testing with
the real problem/error... thx, GetMem.

--Dietmar

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balazsszekely · 2021-09-30 18:00

@dietmar
QuoteOk, after adding the form the the loadings, one can start testing
with the real problem/error... thx, GetMem.
See attached project. Instead of TdbHelper(TForm), please use a
TDataModule.

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dietmar · 2021-09-30 18:29

Thanks a lot for your efforts!
And I will start to read into TDataModule now...

--Dietmar