title: How to use "criteria" methods in Mongoid with Rails 3
body: <p>I'd like to use the Mongoid criteria methods ( <a href="http://mongoid.org/docs/querying/criteria.html" rel="nofollow">http://mongoid.org/docs/querying/criteria.html</a> ).  I have a model named College. In the College controller:</p>
  
  <pre><code>def index
    @colleges = College.all_of(:sat_rmw.gt =&gt; 1200, :in_state_tuition.lt =&gt; 12000)
  end
  </code></pre>
  
  <p>This generates the error:</p>
  
  <blockquote>
    <p>undefined method `all_of' for College:Class</p>
  </blockquote>
  
  <p>Am I supposed to use criteria in the College Model as opposed to the Controller?  Thanks in advance!</p>