角 - 正確使用RXJS展開運算符進行遞歸http調用

Question

我正在嘗試使用前一個調用的值對Reddit的API進行遞歸http調用。問題在於之前的呼叫在下一個呼叫開始之前沒有完成，因此正在進行重複呼叫。應該爲每次調用更新「after」值，直到「after」值未定義爲止。我發現這個related post，並試圖使用所描述的解決方案，但我無法弄清楚如何在下次調用之前確保先前的調用已完成。下面是我的實際代碼：

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會導致遞歸膨脹。爲了解決這個問題，你需要分開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()); 
    } 

要停止擴展您可以使用Observable.empty()。請參閱此post。