How can I add fields to a clientdataset at runtime?

Question

I have a TClientDataSet, which is provided by a TTable’s dataset. The dataset has two fields: postalcode (string, 5) and street (string, 20)

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Answer 1

You should use CreateDataset after add field:

cds.SetProvider(Table1);
cds.FieldDefs.Add('city', ftString, 20);
cds.CreateDataset; 

cds.Open;
cds.Edit;
cds.FieldByName('city').AsString := 'Test';  
cds.Post;