Author: Tomas Rutkauskas

TClientDataSet: Temporary vs. permanent indices

Answer:

On TClientDataSets, that are not connected to a provider but loaded as local text 
files, ('thin client in brief-case mode'), you cannot use TQuerys. You may use the 
Filter property to select data and use an index to sort.

This sample code shows how to create a temporary index (not saved by SaveToFile())
and how to create a permanent index (saved by SaveToFile()):
1   
2   with ClientDataSet1 do
3   begin
4     Close;
5     // Define the fields
6     FieldDefs.Clear;
7     FieldDefs.Add('Project', ftInteger, 0, True);
8     FieldDefs.Add('Number', ftInteger, 0, False);
9     // [..]
10    // Define the PERMANENT index - it is saved with SaveToFile()
11    IndexDefs.Clear;
12    IndexDefs.Add('IProject', 'Project', [ixPrimary, ixUnique]);
13    // Create the dataset
14    CreateDataSet;
15    Open;
16    // the following temporary index is not saved
17    // with data when using SaveToFile()
18    AddIndex('TempIndex', 'Number;Project', [ixPrimary, ixUnique]);
19  end { with ClientDataSet1 }