角 - 正确使用RXJS展开运算符进行递归http调用

Question

我正在尝试使用前一个调用的值对Reddit的API进行递归http调用。问题在于之前的呼叫在下一个呼叫开始之前没有完成，因此正在进行重复呼叫。应该为每次调用更新“after”值，直到“after”值未定义为止。我发现这个related post，并试图使用所描述的解决方案，但我无法弄清楚如何在下次调用之前确保先前的调用已完成。下面是我的实际代码：

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); 
     }); 

Answer 1

返回相同的功能getSavedPostsForAuthenticatedUser会导致递归膨胀。为了解决这个问题，你需要分开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()); 
    } 

要停止扩展您可以使用Observable.empty()。请参阅此post。