Angular firebase 2如何根据子节点中的父按键获取所有子节点详细信息？

import { Component } from '@angular/core';
import { AngularFireDatabase, AngularFireList } from '@angular/fire/database';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-your-component',
  templateUrl: './your-component.component.html',
  styleUrls: ['./your-component.component.css']
})
export class YourComponent {
  itemsRef: AngularFireList<any>;
  items: Observable<any[]>;

  constructor(private db: AngularFireDatabase) {
    this.itemsRef = db.list('your-collection');
    this.items = this.itemsRef.valueChanges();
  }
}

<ul>
  <li *ngFor="let item of items | async">
    {{ item.name }} - {{ item.description }}
  </li>
</ul>