title: Mongoid query! Combination of limit and order
body: <p>In my rails app I want to grab the 10 last records with a unique value.</p>
  
  <p>I tried:</p>
  
  <pre><code>@users = User.all(:limit =&gt; 10, :sort =&gt; [:created_at, :desc]).map{|t| t.first_name}.uniq
  </code></pre>
  
  <p>but,</p>
  
  <p>the limit doesn't work as I expect.. </p>
  
  <p>I want the 'limit' to effect the query last.</p>
  
  <p>any ideas?</p>