title: get counter nested model mongoid
body: <p>2 models:</p>
  
  <pre><code>Class User
   include Mongoid::Document
   has_many :reports
  end
  
  Class Report
   include Mongoid::Document
   belongs_to :user
  end
  </code></pre>
  
  <p>I need a query to get all users have 6 or more reports, something like:.</p>
  
  <pre><code>Users.where(reports.count &gt; 5)
  </code></pre>
  
  <p>I use mongo id 2.4.12</p>
  
  <p>How can I do it?</p>
  
  <p>Thank you very much!</p>