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 to setup the dataset's table structure and how to load data into it at runtime. But when I tried to follow its instructions in D2009, step 4 (table.Open) raised an exception. It said that it didn't have a provider specified.

The entire point of the example on that page is to build a dataset that doesn't need a provider. Is the page wrong, is it outdated, or am I missing a step somewhere? And if the page is wrong, what do I need to use instead to create a completely independent in-memory dataset? I've been using TJvMemoryData, but if possible I'd like to reduce the amount of extra dependencies that my dataset adds into my project.

Solution 1

At runtime you can use table.CreateDataset or if this is on a design surface you can right click on the CDS and click create dataset. You need to have specified columns/types for the CDS before you can do this though.

Solution 2

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

Solution 3

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.

Solution 4

You can use table.CreateDataSet

Solution 5

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)

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