TClientDataset gives access violation when open

[ChrisChuah 0]

Hi

I am having a problem with this function. When issued a ClientDataset.open, the Before Open event is triggered but before the After event is triggered, it returned an Access violation

 

==== Access Violation Log =====

22-12-7 14:46:48-10.100.252.26> LoadTableData2 SQL: SELECT ROW_ID,CREATED_AT,CREATED_BY,FIDSID,AODBID,EVENT,FLIGHT,DOMINT,SDT,TABLENAME,TABLENUMBER,XMLFILE FROM DYNAFLTS
 WHERE (CREATED_AT>=1670342400 and CREATED_AT<1670428800)

<22-12-7 14:46:48-10.100.252.26> cdsDYNAFLTS Before Open
<22-12-7 14:46:48-10.100.252.26> Error in LoadFilterTable: Access violation at address 00F5CC2B in module 'FidsEventViewer.exe'. Read of address 00000000
<22-12-7 14:46:48-10.100.252.26> App Exception: cdsDYNAFLTS: Cannot perform this operation on a closed dataset
=== =========

 

==== Normal log on other machine ====

<7/12/2022 2:53:56 pm-192.168.0.124> LoadTableData2 SQL: SELECT ROW_ID,CREATED_AT,CREATED_BY,FIDSID,AODBID,SDT,FLIGHT,DOMINT,TABLENAME,EVENT,XMLFILE FROM DYNAFLTS
 WHERE (CREATED_AT>=1670342400 and CREATED_AT<1670428800)

<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS Before Open
<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS Start AfterOpen
<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS Start read INI
<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS End read INI
<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS Assign Field to process
<7/12/2022 2:53:56 pm-192.168.0.124> cdsDYNAFLTS End AfterOpen
=============

 

In my code, the SQL is added to TQuery

The Client dataset is link to the Provider. The provider is linked to TQuery.

 

This application is run on another machine without this error but always gives an access violation on this machine.

Is there a "cache" file that ClientDataset would read after the BeforeOpen event?

 

Please advise

regards

chris

 

[programmerdelphi2k 237]

3 hours ago, ChrisChuah said:

App Exception: cdsDYNAFLTS: Cannot perform this operation on a closed dataset

my tip: verify all points where your "query/clientdataset" is used! try verify if exists any try to access/changes state (open/close/edit/etc...)!

it's not easy think if none code is showed

[ChrisChuah 0]

hi

attached is the code whereby it generated the error.

The funny thing is that this app can run on other machines without error but only that particular machine.

 

procedure TDataModule1.loadFilterTable;
var
  l_str : string;
  l_ini : TIniFileEx;
  l_fieldList : string;
begin
  if (trim(FFilterDay) = '') and (Trim(FFilterOthers) = '') then
    l_str := ''
  else if (Trim(FFilterDay) = '') and (Trim(FFilterOthers) <> '') then
    l_str := Trim(FFilterOthers)
  else if (Trim(FFilterDay) <> '') and (Trim(FFilterOthers) = '') then
    l_str := Trim(FFilterDay)
  else
    l_str := Trim(FFilterDay) + ' and ' + Trim(FFilterOthers);
  cdsDYNAFLTS.Close;
  qyDYNAFLTS.Close;
  if DataModule1.getLoginSuccess then begin
    try
      cdsDYNAFLTS.IndexName := '';
      cdsDYNAFLTS.Filter := '';
      cdsDYNAFLTS.Filtered := false;
      qyDYNAFLTS.SQL.Clear;
      l_Ini := TIniFileEx.create(ChangeFileExt(Application.ExeName, '.ini'));
      l_fieldList := l_ini.ReadString(DYNAFLTS_TABLE, INI_SECT_FIELDS, '');
      // cc : if the field list is still empty, then make it a *
      if Trim(l_fieldList) = '' then
        l_fieldList := '*';
      l_ini.Free;
      qyDYNAFLTS.SQL.Add('SELECT ' + l_fieldList + ' FROM ' + DYNAFLTS_TABLE );
      if l_str <> '' then
        qyDYNAFLTS.SQL.Add(' WHERE ' + l_str);
      DoLog('LoadTableData2 SQL: ' + qyDYNAFLTS.SQL.Text);
      cdsDYNAFLTS.ProviderName := '';
      cdsDYNAFLTS.ProviderName := 'dspDYNAFLTS';
      cdsDYNAFLTS.Active := true; <== when open is called, the BeforeOpen will be logged. However the afterOpen is not called
    except
      on e:Exception do begin
        if not CheckDBConnectionError(e.message) then
          DoLog('Error in LoadFilterTable: ' + e.message); <== this will log down the access violation as shown int he log
      end;
    end;
  end;

end;
 

[programmerdelphi2k 237]

when using "TClientDataset" you can needs a "Midas" dll, if you dont compile with MidasLib in your project!

program Project1;

uses
  MidasLib,  // <--- adding this, you'll dont needs DLL to MIDAS on target PC
  Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.