在Angfirefire2中加入Firebase查询 [英] 'Joining' Firebase Queries in Angularfire2

问题描述

更新：

我遇到的空值字段与我的数据库中不存在的键有关，所以大部分的话语赢得了适用于你的问题。如果您正在寻找一种在AngularFire2中加入查询的方法，那么接受的答案在这方面做得很好。我目前使用 combineLatest 而不是 forkJoin 。为了做到这一点你必须 import'rxjs / add / observable / combineLatest'; 。

以下非规范化的Firebase结构：

$ p $ 成员
-memberid1
-threads
-threadid1： true，
-threadid3：true
-username：Adam
...

线程
-threadid1
- 作者：memberid3
-quality：67
-participants
-memberid2：true，
-memberid3：true
...


我想在 threads中显示 username 视图，按 quality 排序。

我的服务：

  getUsername（memberKey：string）{
 return this.af.database.object（'/ members /'+ memberKey +'/ username'）
} 
 
 getFeaturedThreads（）：FirebaseListObservable< any []> {
 return this.af.database.list（'/ threads'，{
 query：{
 orderByChild：'quality'，
 endAt：10 
} 
}）; 
 
 
 
 
 
 
我的组件：
 
 < pre $  ngOnInit（）{
 this.threads = this.featuredThreadsService.getFeaturedThreads（）
 this.threads.subscribe（
 allThreads => 
 allThreads.forEach（thisThread => {
 thisThread.username = this.featuredThreadsService.getUsername（thisThread.author）
 console.log（thisThread.username）
}）
）
} 
  

由于某些原因，这个日志看起来像是没有实现的可观察对象。

我想要得到这些值到 threads 的属性中，所以我可以像这样在我的视图中渲染它：

 < div * ngFor =let thread of thread | asyncclass =thread-tile> 
 ... 
 {{threads.username}} 
 ... 
< / div> 
  

更新： console.log for allThreads 和 thisThread

更新：订阅getUsername（）

  this.featuredThreadsService.getUsername（thisThread.author）
 .subscribe（username => console。日志（用户名））
  

这个结果是没有值的对象：

解决方案

您可以编写一个基于 getFeaturedThreads 查询成员的观察值，并将每个线程的参与者属性中的值替换为用户名：

$ b

 从'rxjs / Observable'导入{Observable}; 
导入'rxjs / add / observable / forkJoin'; 
导入'rxjs / add / operator / do'; 
导入'rxjs / add / operator / first'; 
 import'rxjs / add / operator / switchMap'; 
 
 let featuredThreadsWithUserNames = this.getFeaturedThreads（）
 
 //每当getFeaturedThreads发出时，切换到取消订阅/忽略
 //任何挂起的成员查询：
 
 .switchMap（threads => {
 
 //将线程映射到将被
 //加入的观测值数组当observables发出一个值，更新线程
 
 let memberObservables = []; 
 threads.forEach（thread => {
 
 //添加作者：
 
 memberObservables.push（this.af.database 
 .object（`members / $ {thread.author}`）
 .first（）
 .do（value => {thread.author = value.username;}）
）; 
 
 //添加参与者：
 
 Object.keys（thread.participants）.forEach key => {
 memberObservables.push（this.af.database 
 .object（`members / $ {key}`）
 .first（）
 .do（value => {thread.participants [key] = value.username; }）
）; 
}）; 
}）; 
 
 //加入成员observables，并使用结果选择器
 //返回将被更新的线程。 
 
 return Observable.forkJoin（... memberObservables，（）=> threads）; 
}）; 
  

这会给你一个每次发出 getFeaturedThreads 发出。但是，如果用户名称更改，则不会重新发出。如果这很重要，用 combineLatest 来替换 forkJoin ，并移除 first 运算符从组成的成员observables。

Update:

The issues I was encountering with the empty value fields had to do with non-existent keys in my database, so most of the discourse here won't apply to your question. If you're looking for a way to 'join' queries in AngularFire2, the accepted answer below does a fine job of this. I'm currently using combineLatest instead of forkJoin. In order to do this you have to import 'rxjs/add/observable/combineLatest';.

I have the following denormalized Firebase structure:

members
  -memberid1
    -threads
       -threadid1: true,
       -threadid3: true
    -username: "Adam"
    ...

threads
  -threadid1
      -author: memberid3
      -quality: 67
      -participants
         -memberid2: true,
         -memberid3: true
     ...

I want to render username in my threads view, which is sorted by quality.

My service:

getUsername(memberKey: string) {
    return this.af.database.object('/members/' + memberKey + '/username')
}

getFeaturedThreads(): FirebaseListObservable<any[]> {
    return this.af.database.list('/threads', {
        query: {
            orderByChild: 'quality',
            endAt: 10
        }
    });
}

My component:

ngOnInit() {
    this.threads = this.featuredThreadsService.getFeaturedThreads()
    this.threads.subscribe( 
        allThreads => 
        allThreads.forEach(thisThread => {
            thisThread.username = this.featuredThreadsService.getUsername(thisThread.author)
            console.log(thisThread.username)
        })
    )
} 

For some reason this logs what looks like unfulfilled observables to the console.

I'd like to get these values into a property of threads so I can render it in my view like this:

<div *ngFor="let thread of threads | async" class="thread-tile">
    ...
    {{threads.username}}
    ...
</div>

Updated: console.log for allThreads and thisThread

Updated: subscribed to getUsername()

this.featuredThreadsService.getUsername(thisThread.author)
        .subscribe( username => console.log(username))

The result of this is objects with no values:

解决方案

You can compose an observable based on getFeaturedThreads that queries members and replaces the values in each thread's participants property with user names:

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/forkJoin';
import 'rxjs/add/operator/do';
import 'rxjs/add/operator/first';
import 'rxjs/add/operator/switchMap';

let featuredThreadsWithUserNames = this.getFeaturedThreads()

  // Each time the getFeaturedThreads emits, switch to unsubscribe/ignore
  // any pending member queries:

  .switchMap(threads => {

    // Map the threads to the array of observables that are to be
    // joined. When the observables emit a value, update the thread.

    let memberObservables = [];
    threads.forEach(thread => {

      // Add the author:

      memberObservables.push(this.af.database
        .object(`members/${thread.author}`)
        .first()
        .do(value => { thread.author = value.username; })
      );

      // Add the participants:

      Object.keys(thread.participants).forEach(key => {
        memberObservables.push(this.af.database
          .object(`members/${key}`)
          .first()
          .do(value => { thread.participants[key] = value.username; })
        );
      });
    });

    // Join the member observables and use the result selector to
    // return the threads - which will have been updated.

    return Observable.forkJoin(...memberObservables, () => threads);
  });

This will give you an observable that emits each time getFeaturedThreads emits. However, if the user names change, it won't re-emit. If that's important, replace forkJoin with combineLatest and remove the first operator from the composed member observables.

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