Delphi: using TClientDataset as an in-memory dataset

Question

According to this page, it\'s possible to use TClientDataset as an in-memory dataset, completely independent of any actual databases or files. It describes how

Answer 1

If it helps further, here is a piece of code where I created a ClientDataset that is used as an in-memory table:

procedure TfrmPRMain.ConfigureDataset;
begin
  With cdsMain do begin
    FieldDefs.Add('bDelete', ftBoolean);
    FieldDefs.Add('sSource', ftString, 10);
    FieldDefs.Add('iSection', ftInteger);
    FieldDefs.Add('iOrder', ftInteger);
    FieldDefs.Add('sBranch', ftString, 10);
    FieldDefs.Add('sPulseCode', ftString, 10);
    FieldDefs.Add('sCode', ftString, 10);
    FieldDefs.Add('dtWorkDate', ftDate);
    FieldDefs.Add('iWorkWeek', ftInteger);
    FieldDefs.Add('sName', ftString, 50);
    CreateDataSet;
    LogChanges := False;
    Open;
  end;
end;

You can just substitute your own data information and go. Jack

Answer 2

The code from this page doesn't work in ANY Delphi version. A call to CreateDataSet already puts the dataset into active state ("opened"). You should use .CreateDataSet OR .Open. Not both.

Use .Open when you want to fetch data from a Provider (via ProviderName property) and .CreateDataSet when you want to populate the Dataset by yourself.

BTW: For an in depth reference about ClientDataSets and its features take a look on excellent Cary Jensen articles on CodeGear Developer Network (read the oldest ones, first)

Answer 3

If you'd like a dependency-free, high quality, and feature rich (not to mention free!) in-memory dataset, I highly recommend kbmMemTable. Does everything TClientDataset does and then some.

Answer 4

for some reason this is not working for me. I perform CreateDataset in design time, but it still crashes application. That is still unknown for me. One warning. DO NOT DO THIS:

XXXClientDataSet.Close;
XXXClientDataSet.Open;

because it will report error. Instead of Open, use

xxxClientDataSet.CreateDataset;

In my application I needed to reset data and load it again, and that again caused error message.

Answer 5

Don't forget to include MIDAS.DLL in your installation or simply include MidasLib in uses clause. Otherwise using TClientDataSet will raise an error on client's machine. Maybe it's obvious, but I actually forgot this once.