Question

我有一个函数，它从一个项目数组（myItemsArray）创建一个Observables数组（batchOfRequests）。每个myItem使用myItem属性（propertyOne，propertyTwo等）中的两个参数推送一个Observable（http请求）然后使用Observable.concat在batchOfRequests中为每个Observable发出请求。这工作正常，我可以在returnedData中看到每个请求返回的数据。但是，此时，我不知道myItemsArray中的哪个myItem属于每个请求。有没有办法将每个myItem链接或映射到推入batchOfRequests的Observable？

performMultipleRequests(): void
{
let batchOfRequests: Observable<any>[] = [];

for (let myItem of this.myItemsArray)
{            

this.batchOfTrendRequests.push(this.myService.makeHTTPCall(myItem.propertyOne, myItem.propertyTwo))

}

this.batchOfRequests = this.batchOfRequests.map(obs =>
{
    return obs.catch(err => Observable.of(err));
});       

Observable.concat(...this.batchOfRequests)
    .finally(() =>
    {
        return;
    })
    .subscribe((returnedData: any) =>
    {
        // do something with my returned data... but I need myItem information as well
        return;
    }), (error) =>
    {
            return;
    }
}

Answer 1

forkJoin将以与myItemsArray相同的顺序发出一系列响应。因此，您可以根据其数组索引将每个响应匹配回其请求：

performMultipleRequests(): void {
  let batchOfRequests: this.myItemsArray.map(myItem => 
    this.myService.makeHTTPCall(myItem.propertyOne, myItem.propertyTwo)
      .catch(err => Observable.of(err))
  );

  Observable.forkJoin(...batchOfRequests).subscribe((myResponsesArray: any[]) => {
    myResponsesArray.forEach((returnedData, index) => {
      // lookup myItem corresponding to this returnedData
      const myItem = this.myItemsArray[index];
      ...
    });
  });
}

请注意，使用.catch()可确保部分失败不会导致整批失败。

Answer 2

您可以在推送到阵列之前映射所需的数据。像这样：

let batchOfRequests: Observable<{ myData: any, httpResponse: any }>[] = [];
for (let myItem of this.myItemsArray)
{
    const httpRequest = this.myService.makeHTTPCall(myItem.propertyOne, myItem.propertyTwo);
    const mappedRequest = httpRequest.map(res => { 
        return { myData: myItem, httpResponse: res };
    });

    batchOfRequests.push(mappedRequest);
}

而不是在填充数组后使用map，你也可以在循环中进行错误捕获：

let mappedRequest = httpRequest.map(res => { 
    return { myData: myItem, httpResponse: res };
});

mappedRequest = mappedRequest.catch(err => Observable.of(err));

Answer 3

您可以使用async / wait，如下所示，

优点是

这简单（没有花哨的东西）
并行执行请求
它将按顺序返回值，因此0保证值为0,1推送承诺返回1等。

点击此处：JavaScript Demo: Promise.all()

async/wait in trypscript

async performMultipleRequests(): void
{
  let batchOfRequests: Promise<any>[] = [];

  for (let myItem of this.myItemsArray)
  {            
    this.batchOfTrendRequests.push
      (this.myService.makeHTTPCall
         (myItem.propertyOne, myItem.propertyTwo).toPromise());

  }
  //this will return you array of all completed request
  const allRetunValue = await Promise.all(batchOfTrendRequests);

  allRetunValue.forEach(retval=> { console.log(retval); }); 
}

如何映射或访问Observables数组（http请求）的输入

3 个答案: