선생님 v6에서 groupingBy에 o객체를 참조 못합니다..ㅠㅠ

# OrderQueryDto

@Data
public class OrderQueryDto {

    private Long orderId;
    private String name;
    private LocalDateTime orderDate;
    private OrderStatus orderStatus;
    private Address address;
    private List<OrderItemQueryDto> orderItems;

    public OrderQueryDto(Long orderId, String name, LocalDateTime orderDate, OrderStatus orderStatus, Address address) {
        this.orderId = orderId;
        this.name = name;
        this.orderDate = orderDate;
        this.orderStatus = orderStatus;
        this.address = address;
    }

    public OrderQueryDto(Long orderId, String name, LocalDateTime orderDate, OrderStatus orderStatus, Address address, List<OrderItemQueryDto> orderItems) {
        this.orderId = orderId;
        this.name = name;
        this.orderDate = orderDate;
        this.orderStatus = orderStatus;
        this.address = address;
        this.orderItems = orderItems;
    }
}

# OrderFlatDto

@Data
public class OrderFlatDto {

    private Long orderId;
    private String name;
    private LocalDateTime orderDate; //주문시간
    private Address address;
    private OrderStatus orderStatus;

    private String itemName;//상품 명
    private int orderPrice; //주문 가격
    private int count; //주문 수량

    public OrderFlatDto(Long orderId, String name, LocalDateTime orderDate, OrderStatus orderStatus, Address address, String itemName, int orderPrice, int count) {
        this.orderId = orderId;
        this.name = name;
        this.orderDate = orderDate;
        this.orderStatus = orderStatus;
        this.address = address;
        this.itemName = itemName;
        this.orderPrice = orderPrice;
        this.count = count;
    }
}

# Tried to fix...

@GetMapping("/api/v6/orders")
public List<OrderQueryDto> ordersV6() {
    List<OrderFlatDto> flats = orderQueryRepository.findAllByDto_flat();

    return flats.stream()
            .collect(groupingBy(o -> new OrderQueryDto(o.getOrderId(), o.getName(), o.getOrderDate(), o.getOrderStatus(), o.getAddress()),
                    mapping(o -> new OrderItemQueryDto(o.getOrderId(), o.getItemName(), o.getOrderPrice(), o.getCount()), toList())
            )).entrySet().stream()
            .map(e -> new OrderQueryDto(e.getKey().getOrderId(), e.getKey().getName(), e.getKey().getOrderDate(), e.getKey().getOrderStatus(), e.getKey().getAddress(), e.getValue()))
            .collect(toList());
}