AngularFire2 - 嵌套的FirebaseObjectObservable不会触发嵌套的Firebase调用 [英] AngularFire2 - nested FirebaseObjectObservable won't fire a nested Firebase call

问题描述

我有一个处理与Firebase中的多对多关系的问题。基本上，我试图从我的Firebase数据中的多个路径构建一个用户配置文件对象。我试过构建一个函数，返回一个observable，然后更新该observable中的数据，作为嵌套的observable从Firebase获取数据。

问题是嵌套的observable从我所知道的情况来看，它们从来没有被召唤过。我几个小时没有取得任何真正的成功，一直在殴打我的头。任何人都可以告诉我做错了什么？我感觉这是一个很常见的问题，得到解决。

  public getUserProfile（data）{
 
返回this._af.database.object（`/ social / users / $ {data.id}`）.map（（user）=> {
 for（let user.videos中的vidKey）{
 
 //一旦代码到达这一行，就不会触发:( 
 this._af.database.object（`/ social / videos / $ {vidKey}`）.map（（video ）=> {
 user.videos [vidKey] = video; 
}）; 
} 
返回用户; 
}）; 
} 
  

解决方案

嵌套的observable永远不会被调用，因为它永远不会被订阅 - 你可以做这样的事情，而不是：

  public getUserProfile（data）{
 
 return this._af.database 
 .object（`/ social / users / $ {data.id}`） 
 
 //切换到加入可观察的
 
 .switchMap（（user）=> {
 
 let vidKeys = Object.keys（user.videos）; 
 
 //使用forkJoin加入视频观察对象。可观察到的
 //需要完成，所以首先使用。并使用forkJoin的选择器
 //将视频映射到用户，然后返回用户。 
 $ b $ return Observable.forkJoin（
 vidKeys.map（（vidKey）=> this._af.database 
 .object（`/ social / videos / $ {vidKey}` ）
 .first（）
），
（... videos）=> {
 vidKeys.forEach（（vidKey，index）=> {user.videos [ vidKey] = videos [index]}）; 
返回用户; 
} 
）; 
}）; 
} 
  

I've got a question about dealing with working with many-to-many relationships in Firebase. Basically, I'm trying to build a user profile object from multiple paths inside of my Firebase data. I've tried building a function that returns an observable and then updates the data in that observable as a nested observable grabs data from Firebase.

The problem is that the nested observable doesn't ever get called, from what I can tell. I've been beating my head against this for hours without any real success. Can anyone tell what I'm doing wrong? I feel this is a pretty common problem that gets solved.

public getUserProfile(data) {

    return this._af.database.object(`/social/users/${data.id}`).map((user) => {
        for ( let vidKey in user.videos) {

            // Once the code hits this line, it never fires at all :(
            this._af.database.object(`/social/videos/${vidKey}`).map((video) => {
                user.videos[vidKey] = video;
            });
        }
        return user;
    });
}

解决方案

The nested observable is never called because it's never subscribed to - observables are lazy.

You could do something like this, instead:

public getUserProfile(data) {

  return this._af.database
    .object(`/social/users/${data.id}`)

    // Switch to the joined observable

    .switchMap((user) => {

      let vidKeys = Object.keys(user.videos);

      // Use forkJoin to join the video observables. The observables will
      // need to complete, so first is used. And use forkJoin's selector to
      // map the videos to the user and then return the user.

      return Observable.forkJoin(
        vidKeys.map((vidKey) => this._af.database
          .object(`/social/videos/${vidKey}`)
          .first()
        ),
        (...videos) => {
          vidKeys.forEach((vidKey, index) => { user.videos[vidKey] = videos[index] });
          return user;
        }
      );
    });
}

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