title: How do I create a hot RX observable from multiple DBContexts
body: <p>DBContexts are short lived, created and destroyed with every request. I have a number of tasks that I'd like to perform prior to and post save and I'd like to handle these with some sort of eventing model. I'm wondering in RX is the right route.</p>
  
  <p>Is there some way of creating a singleton "hub" then causing my DBContext to raise BeforeChange (SavingChanges event) and post save (no applicable event) Observables and "push" them into the long lived hub.</p>
  
  <p>In effect I'd like to do this in my "hub" singleton</p>
  
  <pre><code>    public IObservable&lt;EventPattern&lt;EventArgs&gt;&gt; Saves = new Subject&lt;EventPattern&lt;EventArgs&gt;&gt;();
  
      public void AttachContext(DbContext context)
      {
          Saves = Observable.FromEventPattern&lt;EventArgs&gt;(((IObjectContextAdapter)context).ObjectContext, "SavingChanges");
      }
  </code></pre>
  
  <p>but in such a way that AttachContext simply feed its generated observable into the exisitng Saves observabe, rather than replacing it (and all of its subscriptions)?</p>