使用 forkjoin 合并 http observables

问题描述

我试图通过使用 forkjoin 来避免嵌套的 observables.当前(嵌套)版本如下所示:

I'm trying to avoid nested observables by using forkjoin. The current (nested) version looks like this:

  this.http.get('https://testdb1.firebaseio.com/.json').map(res => res.json()).subscribe(data_changes => {
    this.http.get('https://testdb2.firebaseio.com/.json').map(res => res.json()).subscribe(data_all => {
      /* Do this once resolved */
      this.platform.ready().then(() => {
        this.storage.set('data_changes', data_changes);
        this.storage.set('data_all', data_all);
        document.getElementById("chart").innerHTML = "";
        this.createChart();
      });
    });
  },

    err => {
      this.platform.ready().then(() => {
        console.log("server error 2");
        document.getElementById("chart").innerHTML = "";
        this.createChart();
      });
    });
  }

我可以将第一部分改写为:

I can rewrite the first part as:

Observable.forkJoin(
  this.http.get('https://testdb1.firebaseio.com/.json').map((res: Response) => res.json()),
  this.http.get('https://testdb2.firebaseio.com/.json').map((res: Response) => res.json())
)

但我不确定如何添加 .subscribe 方法来访问 data_changes 和 data_all.

But i'm not sure how I would then add the .subscribe method to access both data_changes and data_all.

再看另一个例子，我知道它应该类似于 .subscribe(res => this.combined = {friends:res[0].friends, customer:res[1]});，但我不确定如何使其适应我的示例.

Looking at another example, I know it should look something like .subscribe(res => this.combined = {friends:res[0].friends, customer:res[1]});, but i'm not sure how to adapt this to my example.

推荐答案

尝试使用 combineLatest 代替 forkJoin :

Try to use combineLatest instead of forkJoin :

与 combineLatest :

With combineLatest :

const combined = Observable.combineLatest(
  this.http.get('https://testdb1.firebaseio.com/.json').map((res: Response) => res.json()),
  this.http.get('https://testdb2.firebaseio.com/.json').map((res: Response) => res.json())
)

combined.subscribe(latestValues => {
    const [ data_changes , data_all ] = latestValues;
    console.log( "data_changes" , data_changes);
    console.log( "data_all" , data_all);
});

你也可以通过 forkJoin 来处理，但是 forkJoin 会在所有调用完成后返回数据并返回结果，但是在 combineLatest 中任何一个 observable 发出一个值时，都会从每个中发出最新的值.

You can also handle it by forkJoin , but forkJoin will return data when all calls are finished and return result , but in combineLatest When any observable emits a value, emit the latest value from each.

使用 forkJoin :

With forkJoin :

const combined = Observable.forkJoin(
  this.http.get('https://testdb1.firebaseio.com/.json').map((res: Response) => res.json()),
  this.http.get('https://testdb2.firebaseio.com/.json').map((res: Response) => res.json())
)

combined.subscribe(latestValues => {
    const [ data_changes , data_all ] = latestValues;
    console.log( "data_changes" , data_changes);
    console.log( "data_all" , data_all);
});

调用两者并检查控制台日志，你会明白的.

Call both and check the console log , you will get idea.

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