TFDMemTable lost/clearing data after filtering - delphi

Question

I have created a FDMemTable with following structure:
Cds_NaMenu := TFDMemTable.Create(nil);
Cds_NaMenu.FieldDefs.Add('ID', ftInteger);
Cds_NaMenu.FieldDefs.Add('MN_TELA_CODIGO', ftInteger);
Cds_NaMenu.FieldDefs.Add('MN_MENU_PESQUISA', ftString, 500);
Cds_NaMenu.FieldDefs.Add('DISPONIBILIDADE', ftInteger);
Cds_NaMenu.IndexDefs.Add('Ordem', 'MN_TELA_CODIGO', []);
Cds_NaMenu.CreateDataSet;
Cds_NaMenu.LogChanges := False;
Cds_NaMenu.IndexName := 'Ordem';
I put data in TFDMemTable like this:
Cds_NaMenu.Append;
Cds_NaMenu.FieldByName('DISPONIBILIDADE').AsInteger := 1;
Cds_NaMenu.Post;
Well... The problem ocurrs when a set filtered property to True and back to False. The RecordCount property goes to 0; None data has found in, even I use saveToFile procedure. Aparently the data was losted.
_recCount := Cds_NaMenu.RecordCount; // Result = 867;
Cds_NaMenu.Filter := 'DISPONIBILIDADE=1 AND MN_MENU_PESQUISA like ' + QuotedStr('%' + sTexto + '%');
Cds_NaMenu.Filtered := True;
_recCount := Cds_NaMenu.RecordCount; // Result = 0;
Cds_NaMenu.Filtered := False;
Cds_NaMenu.Filter := '';
_recCount := Cds_NaMenu.RecordCount; // Result = 0;
PS: With ClientDataSet, this code works perfectly

Answer 1

If you're working with a pure memory table, there should not be any problem to query record count by the RecordCount property. Maybe you expect having NULL and empty value records included in a filtered view when having filter Value LIKE '%%', but it's not so. When having dataset like this:
ID | Value
1 | NULL
2 | ''
3 | 'Some text'
And applying filter like this:
var
S: string;
begin
S := '';
FDMemTable.Filtered := False;
FDMemTable.Filter := 'Value LIKE ' + QuotedStr('%' + S + '%');
FDMemTable.Filtered := True;
{ ← FDMemTable.RecordCount should be 1 here for the above dataset }
end;
The empty and NULL value records should not be included in the view. Here is a short proof:
var
S: string;
MemTable: TFDMemTable;
begin
MemTable := TFDMemTable.Create(nil);
try
MemTable.FieldDefs.Add('ID', ftInteger);
MemTable.FieldDefs.Add('Value', ftString, 500);
MemTable.IndexDefs.Add('PK_ID', 'ID', [ixPrimary]);
MemTable.CreateDataSet;
MemTable.AppendRecord([1, NULL]);
MemTable.AppendRecord([2, '']);
MemTable.AppendRecord([3, 'Some text']);
S := '';
MemTable.Filtered := False;
MemTable.Filter := 'Value LIKE ' + QuotedStr('%' + S + '%');
ShowMessage(Format('Total count: %d', [MemTable.RecordCount])); { ← should be 3 }
MemTable.Filtered := True;
ShowMessage(Format('Filtered count: %d', [MemTable.RecordCount])); { ← should be 1 }
MemTable.Filtered := False;
ShowMessage(Format('Total count: %d', [MemTable.RecordCount])); { ← should be 3 }
finally
MemTable.Free;
end;
end;

Answer 2

I think this is just a minor FD quirk. The code below works as expected, with Cds_NaMenu declared as a TFDMemTable (though it would have been nice if you could have dropped the Cds_ to avoid confusion).
The key difference, I think, is the call to .Locate after the filter is cleared. The reason I put it there is because it causes the dataset to scroll and, I imagine, to recalculate its RecordCount as a result. Probably any other operation which causes a scroll would have the same effect, even MoveBy(0) - try it.
procedure TForm1.FormCreate(Sender: TObject);
var
_recCount : Integer;
ID : Integer;
sTexto : String;
begin
sTexto := 'xxx'; // added
Cds_NaMenu.FieldDefs.Add('ID', ftInteger);
Cds_NaMenu.FieldDefs.Add('MN_TELA_CODIGO', ftInteger);
Cds_NaMenu.FieldDefs.Add('MN_MENU_PESQUISA', ftString, 500);
Cds_NaMenu.FieldDefs.Add('DISPONIBILIDADE', ftInteger);
Cds_NaMenu.IndexDefs.Add('Ordem', 'MN_TELA_CODIGO', []);
Cds_NaMenu.CreateDataSet;
Cds_NaMenu.LogChanges := False;
Cds_NaMenu.IndexName := 'Ordem';
Cds_NaMenu.Append;
Cds_NaMenu.FieldByName('ID').AsInteger := 666; // added
Cds_NaMenu.FieldByName('DISPONIBILIDADE').AsInteger := 1;
Cds_NaMenu.Post;
_recCount := Cds_NaMenu.RecordCount; // Result = 1
ID := Cds_NaMenu.FieldByName('ID').AsInteger; // added
Cds_NaMenu.Filter := 'DISPONIBILIDADE=1 AND MN_MENU_PESQUISA like ' + QuotedStr('%' + sTexto + '%');
Cds_NaMenu.Filtered := True;
_recCount := Cds_NaMenu.RecordCount; // Result = 0;
Cds_NaMenu.Filtered := False;
Cds_NaMenu.Filter := '';
// Now force the dataset to scroll
if Cds_NaMenu.Locate('ID', ID, []) then; // added
_recCount := Cds_NaMenu.RecordCount; // Result = 1;
Caption := IntToStr(_recCount); // added
end;