TTestObject1 = Class(TPersistentEx)
  private
    FRechner: Double;
  published
    property Rechner: Double read FRechner write FRechner;
  End;

  TTestObject2 = Class(TPersistentEx)
  private
    FName: String;
    FAlter: Integer;
    FTestObject1: TTestObject1;
  public
    constructor Create;
    destructor Destroy; override;
  published
    property Name: String read FName write FName;
    property Alter: Integer read FAlter write FAlter;
    property TestObject1: TTestObject1 read FTestObject1 write FTestObject1;
  End;

procedure TForm1.Button3Click(Sender: TObject);
var
  TestObject : TTestObject2;
  TestObject2 : TTestObject2;
  m : TMemoryStream;
begin
  TestObject := TTestObject2.Create;
  TestObject2 := TTestObject2.Create;
  m := TMemoryStream.Create;
  try
    with TestObject do begin
       FTestObject1.Rechner := 99.7;
       FName := 'Hallo';
       FAlter := 45;
    end;

    with TestObject2 do begin
       FTestObject1.Rechner := -6.7;
       FName := '';
       FAlter := -1;
    end;
    TestObject.AssignTo(TestObject2);

    TestObject.ToStream(m);
    m.Position := 0;
    TestObject2.FromStream(m);
  finally
    m.Free;
    TestObject.Free;
    TestObject2.Free;
  end;
end;