firebase 和 Ionic 2 上的降序 orderByChild() [英] Descending orderByChild() on firebase and Ionic 2

问题描述

我需要按日期排序的项目，但显然我需要降序排序以正确顺序显示帖子...

I need get items sorted by date, but obviously I need descending sorted to show the posts in correct order...

import {
  AngularFireDatabase
} from 'angularfire2/database';
import 'rxjs/add/operator/map';

/*
  Generated class for the FirebaseProvider provider.

  See https://angular.io/docs/ts/latest/guide/dependency-injection.html
  for more info on providers and Angular 2 DI.
*/
@Injectable()
export class FirebaseProvider {

  constructor(public afd: AngularFireDatabase) {}


  getPostsItems() {
    return this.afd.list('/Posts/', {
      query: {
        orderByChild: "date",
      }
    });

  }

此查询返回升序，我需要 Firebase 网络中未解释的降序.

This query returns a ascendent order and I need a descendent order that it's not explained in Firebase web.

我需要哪些查询?

推荐答案

一种方法是颠倒组件模板中的顺序.首先，您可以直接在组件中获得帖子列表:

One approach could be reversing the order in your component's template. First, you get a list of posts directly in your component:

posts.component.ts

    export class PostsComponent {
      posts: FirebaseListObservable<any>;
     
      constructor(db: AngularFireDatabase) {
        this.posts = db.list('/posts', {
          query: {
            orderByChild: 'date'
          }
        });
      }
    }

然后，您可以使用 reverse 方法来反转您的帖子在模板中的顺序:

Then, you can use the reverse method to reverse your posts' order in your template:

posts.component.html

    <div *ngFor="let post of (posts | async)?.slice().reverse()">
      <h1>{{ post.title }}</h1>
    </div>

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