Sort grid using memory table

Question

I want to sort a grid. I created a memory table and link it to the grid as the data source.I am inserting data to the memory table from a nxQuery object. For the sorting i have to add index as well to the memory table.

This is the index adding and inserting part which is in the form create event

nxMemTable1.IndexDefs.Clear;
nxMemTable1.FieldDefs.Clear;

nxMemTable1.FieldDefs.Add('packpatientid', ftInteger, 0, False);
nxMemTable1.FieldDefs.Add('firstname', ftString, 10, False);
nxMemTable1.FieldDefs.Add('lastname', ftString, 10, False);
while not nxQuery1.EOF do
begin
  nxMemTable1.Append;
  nxMemTable1.FieldByName('packpatientid').AsInteger :=   nxQuery1packpatientid.AsInteger;
  nxMemTable1.FieldByName('firstname').AsString := nxQuery1firstname.AsString;
  nxMemTable1.FieldByName('lastname').AsString := nxQuery1lastname.AsString;
  nxMemTable1.Post;
end;

and this is the code that i am trying to sort the memory table

procedure TForm1.Button2Click(Sender: TObject); begin nxMemTable1.IndexFieldNames := 'firstname'; end;

but this is not working. when i click the button it says "No index for field 'firstname'"

Answer 1

This works with the standard TClientDataSet.

I created a new VCL Forms project, dropped a TClientDataSet on the form, and named it CDS for simplicity in the code. I then added a TDataSource, assigned CDS to its DataSet property, added a TDBGrid, and assigned DataSet1 as its DataSource. I then created two event handlers, one for the Form1.OnCreate event and one for the DBGrid1. OnTitleClick event.

procedure TForm1.DBGrid1TitleClick(Column: TColumn);
var
  sField: string;
begin
  sField := Column.FieldName;
  if sField <> CDS.IndexFieldNames then
    CDS.IndexFieldNames := sField;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  CDS.FieldDefs.Add('LastName', ftString, 30);
  CDS.FieldDefs.Add('FirstName', ftString, 30);
  CDS.FieldDefs.Add('ID', ftInteger);
  CDS.CreateDataSet;
  CDS.AppendRecord(['Smith', 'John', 3]);
  CDS.AppendRecord(['Doe', 'Jane', 1]);
  CDS.AppendRecord(['Adams', 'Quincy', 2]);
  CDS.IndexFieldNames := 'LastName';
end;

Running the application and clicking on any of the column titles immediately sorts the DBGrid by that column (if it's not already sorted by that column).