我正在用Angular和Node.js编写应用程序。我有一个对象（order），它有一个对象（项目）列表，这些对象（项目）也包含对象（产品id列表）。我想把它们全部显示在一个html文件中。请帮帮我。

<div *ngIf="order">
    <div *ngFor="let item of order.items"> // <- it does not work
        <a>{{order.items}}</a> // <--
    </div>
</div>

null

export class AdminOrderItemComponent implements OnInit {
  order: Order;
  orderId;
  constructor(private orderService: OrderService, private route: ActivatedRoute) { }

  ngOnInit() {
    this.route.paramMap
      .subscribe(params => {
        this.orderId = [params.get('id')];
        this.getOrderById();
      });
  }
  getOrderById() {
    this.orderService.getOrderById(this.orderId).subscribe(
      res => {
        this.order = res;
      },
      err => console.log(err)
    );
  }
}

订单界面:

export interface Order  {
  _id: any;
  shipping: string;
  userData: {};
  sum: number;
  items: {};
}