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I have "briefcase model application". Clientdataset reads data from xml-file. After closing modified data are saved in the xml-file. When click on "applyUpdate" button, data are saved in firebird db. If I don't exit program then ApplyUpdate works properly and commits delta-packet in db but sometimes, after closing-opening program 3- 4-5 times, for no clear reason delta becomes empty and after that if I click on "apply" button ApplyUpdates(-1) operator causes exception "access violation". Delphi 10.4, update 2. Firebird3. Project and db files on google drive: https://drive.google.com/drive/folders/1UvtGmaWLdmmSYQITWpEvp-BwRNmw9VEL?usp=sharing unit Unit1; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Data.DB, FireDAC.Stan.Intf, FireDAC.Stan.Option, FireDAC.Stan.Param, FireDAC.Stan.Error, FireDAC.DatS, FireDAC.Phys.Intf, FireDAC.DApt.Intf, FireDAC.Stan.Async, FireDAC.DApt, Datasnap.DBClient, FireDAC.Comp.DataSet, FireDAC.Comp.Client, Datasnap.Provider, Vcl.StdCtrls, Vcl.Buttons, Vcl.ComCtrls, Vcl.Grids, Vcl.DBGrids, FireDAC.UI.Intf, FireDAC.Stan.Def, FireDAC.Stan.Pool, FireDAC.Phys, FireDAC.Phys.FB, FireDAC.Phys.FBDef, FireDAC.VCLUI.Wait, MidasLib; type TForm1 = class(TForm) LabelStatus: TLabel; LabelChangeCount: TLabel; DBGrid: TDBGrid; bApply: TBitBtn; DBGrid2: TDBGrid; bClose: TButton; bOpen: TButton; bMerge: TBitBtn; DataSource1: TDataSource; DataSetProvider1: TDataSetProvider; qGoods: TFDQuery; cdsGoods: TClientDataSet; DataSource2: TDataSource; FDConnection1: TFDConnection; FDTransaction1: TFDTransaction; qGoodsGOODS_ID: TIntegerField; qGoodsGOOD: TWideStringField; qGoodsQNT: TWideStringField; procedure bApplyClick(Sender: TObject); procedure bCloseClick(Sender: TObject); procedure bOpenClick(Sender: TObject); procedure FormCreate(Sender: TObject); procedure cdsGoodsAfterPost(DataSet: TDataSet); procedure DataSource1DataChange(Sender: TObject; Field: TField); procedure FormCloseQuery(Sender: TObject; var CanClose: Boolean); procedure FormClose(Sender: TObject; var Action: TCloseAction); private { Private declarations } public { Public declarations } end; var Form1: TForm1; FN: TFileName; MySavePoint: integer; Modified: boolean; implementation {$R *.dfm} procedure TForm1.FormCreate(Sender: TObject); begin qGoods.Open; FN:= ExtractFilePath(ParamStr(0)) + 'cds.xml'; cdsGoods.filename:= FN; cdsGoods.Close; cdsGoods.open; MySavePoint:= cdsGoods.SavePoint; end; procedure TForm1.bApplyClick(Sender: TObject); begin cdsGoods.ApplyUpdates(-1); qGoods.Refresh; MySavePoint:=cdsGoods.SavePoint; Modified:= false; end; procedure TForm1.bCloseClick(Sender: TObject); begin cdsGoods.Close; end; procedure TForm1.bOpenClick(Sender: TObject); begin cdsGoods.Open; end; procedure TForm1.cdsGoodsAfterPost(DataSet: TDataSet); begin Modified:= true; end; procedure TForm1.DataSource1DataChange(Sender: TObject; Field: TField); begin case cdsGoods.UpdateStatus of usUnmodified: labelStatus.Caption:='record didnt change'; usModified: labelStatus.Caption:='record was modified'; usInserted: labelStatus.Caption:='record was inserted'; usDeleted: labelStatus.Caption:='record was deleted'; end; end; procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction); begin qGoods.close; cdsGoods.Close; end; procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: Boolean); begin if Modified then case application.MessageBox(PwideChar('Data were changed. Save changes?'), '', MB_YESNOCANCEL+MB_ICONQUESTION) of IDCancel: CanClose:=false; IDNo: cdsGoods.SavePoint:=MySavePoint; // IDYES- no needed. Cds is saved auomatically after close // cdsGoods.saveToFile(FN); end; end; end.

Test case information To reproduce the error specific data and specific, a bit complex, nested clientdataset layout is needed. The test is just opening master clientdataset and walking through all its records including nested datasets. Result is written to memo box. To run it click on button Open ClientDataSet. Button Run All Tests for Case ID runs repeated test for all option combinations . Output is saved in app's folder. Each dataset in its own .txt file. The name of the file includes chosen params. For one set of data there is problem retreiving data from database into ClientDataSet component (Case 1 and Case 2). Either there is error on dataset open method and the other has one empty nested dataset where it should be one record present (cdsP40 dataset). Calculated field is added on cdsP47 that is way down the nested hierarchy. This is the only calculated field in the project. It is created at run-time if settings Case Calculated Field Kind requires it. There is no OnCalculated event and calculated field isn't used anywhere. Just defined. Case 1 - missing data record (empty cdsP40 dataset) ID 7367 Fetch on demand PacketRecord = 50 Case 2 - "no current record" ID 7367 fkInternalCalc Fetch All PacketRecord -1 Case 3 - all OK ID 7367 No calculated fields / fkCalculated Fetch All PacketRecord -1 Case 4 - all OK ID 7334 There is a demo application with small mssql database attached. DataSetProviderDemo.zip