Angular-正确使用RXJS扩展运算符进行递归http调用 [英] Angular - Correctly using RXJS expand operator to make recursive http calls

问题描述

我正在尝试使用上一次调用中的值对Reddit的API进行递归http调用.问题在于上一个呼叫在下一个呼叫开始之前尚未完成，因此正在重复进行呼叫.应该为每个调用更新"after"值，直到未定义"after"值.我发现此相关帖子，并尝试使用所描述的解决方案，但是我无法弄清楚如何在下一个呼叫之前确保上一个呼叫已完成.下面是我的实际代码:

I am attempting to make recursive http calls to Reddit's API using a value from the previous call. The problem is that the previous call is not finished before the next one starts, so duplicate calls are being made. The "after" value should be updated for every call until the "after" value is undefined. I found this related post and have attempted to use the solution described, but I can't figure out how to make sure the previous call is finished before making the next call. Below is my actual code:

private getSavedPostsForAuthenticatedUser(username: string, after: string, userPosts: any) {
    const headers = new Headers();
    if (!userPosts) {
        userPosts = [];
    }
    headers.append('Authorization', `Bearer ${this._token}`);
    const redditUrl = `${RetainerConfig.redditOauthUrl}user/${username}/saved`;
    const url = after ? `${redditUrl}/?after=${after}` : redditUrl;
    return this._http.get(url, { headers: headers })
        .map(response => response.json())
        .expand(response => {
            if (response.data) {
                for (const post of response.data.children) {
                    userPosts.push(post);
                }
                if (response.data.after) {
                    return this.getSavedPostsForAuthenticatedUser(username, response.data.after, userPosts);
                }
            }
            return Observable.of(userPosts);
        });

推荐答案

返回相同的函数getSavedPostsForAuthenticatedUser将导致递归扩展.要解决此问题，您需要将http observable分开.

Returning the same function getSavedPostsForAuthenticatedUser will cause recursive expands. To solve this you need to separate the http observable.

  private getSavedPostsForAuthenticatedUser(username: string, after: string, userPosts: any) {
    const request$ = this._getRequest(username, after, userPosts);
    if (!userPosts) {
      userPosts = [];
    }
    return request$
      .expand(response => {
        if (response.data) {
          for (const post of response.data.children) {
            userPosts.push(post);
          }
          if (response.data.after) {
            return this._getRequest(username, response.data.after, userPosts);
          }
        }
        return Observable.of(userPosts);
      });
  }

  private _getRequest(username: string, after: string) {
    const headers = new Headers();
    headers.append('Authorization', `Bearer ${this._token}`);
    const redditUrl = `${RetainerConfig.redditOauthUrl}user/${username}/saved`;
    const url = after ? `${redditUrl}/?after=${after}` : redditUrl;

    return this._http.get(url, {headers: headers})
      .map(response => response.json());
  }

要停止扩展，可以使用Observable.empty().请参阅此帖子.

To stop the expanding you may use Observable.empty(). Please refer to this post.

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