在firebase和Ionic 2上降序orderByChild（） [英] Descending orderByChild() on firebase and Ionic 2

问题描述

我需要按日期排序项目，但显然我需要降序排序以正确的顺序显示帖子...

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",
      }
    });

  }

此查询返回一个上升顺序，我需要一个后代顺序它在Firebase网站中没有解释。

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

一种方法可能是颠倒组件模板中的顺序。首先，您会直接在您的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，您可以使用反转在您的模板中撤消帖子订单的方法：

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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