title: How to Return Observable from inside Observable
body: <p>I have this code that grabs a cached value:</p>
  
  <pre><code>getConfigurations(): Observable&lt;SiteConfiguration[]&gt; {
      return this.storageService.getSiteConfigurations().map(c =&gt; {
          if(c) {
              return c;
          }                         
          return this.httpClient.get&lt;SiteConfiguration[]&gt;(this.url + "/config").subscribe(c =&gt; c);
      });        
  }
  </code></pre>
  
  <p>I cache the <code>SiteConfiguration</code> object, but need to go to the server to get it if it doesn't exist.  But I can't return the second observable inside the first, as it would be returning an <code>Observable&lt;Observable&lt;SiteConfiguration[]&gt;&gt;</code>.  </p>
  
  <p>I'm sure this is a common scenario but my google-fu failed to find an answer.</p>