DELPHI - How to work with TDirectory (generic)

TDictionary is collection of key-value. In this example is it used for saving previous values - and its refreshing.

procedure TSQLParams.LoadForSQL( _iSQL_ID : integer );
var
  i : integer;
  b : boolean;
  vValue : variant;
  pParam : TSQLParam;
  pSQLParam : TSQLParam;
  pOldValues : TDictionary < string, variant >;
begin

  pOldValues := TDictionary < string, variant >.Create;

  try
    { -- save old values of params }

    for i := 0 to self.Count - 1 do
      begin
        pParam := TSQLParam( Items[ i ] );

        if not VarIsNull( pParam.vValue ) then
          pOldValues.Add( pParam.sIdent, pParam.vValue );
      end;

    { -- clear all }

    clear;

    { - get info  }

    if DB_SP.sp_params_by_sql_id.Active then DB_SP.sp__params_by_sql_id.Close;
    DB_SP.sp_params_by_sql_id.ParamByName( '@sql_id' ).AsInteger := _iSQL_ID;
    DB_SP.sp_sql_detail_params_by_sql_id.Open;

    DB_SP.sp_params_by_sql_id.First;
    while not DB_SP.sp_params_by_sql_id.Eof do
      begin
        { create new param }

        pSQLParam := TSQLParam( self.Add );
        pSQLParam.sIdent := DB_SP.sp_params_by_sql_id.FieldByName( 'ident' ).AsString.ToLower;
        pSQLParam.vValue := Variants.null;

       { - try to find old saved value }

       b := pOldValues.TryGetValue( pSQLParam.sIdent, vValue );
       if b then pSQLParam.vValue := vValue;

       { - next row }

       DB_SP.sp_params_by_sql_id.Next;

     end;

  finally
    pOldValues.Free;
  end;

end;