title: Persistent parameter in Rails controller
body: <p>is there any way to persist (preserve) parameters in Rails controller? It should be passed to every action, then to every view and every link.</p>
  
  <p>Example situation:
  I have entity A with its controller. Besides, I have another entity B which is dependent on A. I need to access the "parent" A entity very often, so I'd like to have it still as</p>
  
  <p><code>http://some_url/b_controller/b_action?a_entity=xyz</code></p>