title: How to setup MongoMapper Observer
body: <p>I'm trying to create some mongo mapper observer.
  I found a class exit for that : <a href="http://rubydoc.info/gems/danielharan-mongo_mapper/0.6.5/MongoMapper/Observer" rel="nofollow">http://rubydoc.info/gems/danielharan-mongo_mapper/0.6.5/MongoMapper/Observer</a></p>
  
  <p>The question is how to activate them.</p>
  
  <p>I create an app/observers/admin_observer.rb</p>
  
  <pre><code>class AdminObserver &lt; MongoMapper::Observer
   observe :admin # my admin model
  
   # call backs ...
  end
  </code></pre>
  
  <p>The question now is how to active them ?
  The active record way is :</p>
  
  <pre><code>module MyApp
    class Application &lt; Rails::Application
       config.active_record.observers = :admin
       # other config
    end
  end
  </code></pre>
  
  <p>But with MongoMapper no active_record. Quite naive, I tried config.mongo_mapper.observers = :admin, but their is no observers in mongo_mapper configuration ...</p>
  
  <p>I dunno what to try else and my google research didn't give me a clue.</p>