title: How to use the method 'include?' of the class Mongoid::Criteria?
body: <p>The class document of <a href="http://rdoc.info/github/mongoid/mongoid/Mongoid/Criteria" rel="nofollow">Mongoid::Criteria</a> doesn't mention anything about the method 'include?'. I think it should behave like Array.include?, but it isn't. </p>
  
  <p>Here is an example showing that how an array works.,</p>
  
  <pre><code>months = ['January', 'February', 'March']
  months.include? 'January' #=&gt; true
  months.include? 'Jan'     #=&gt; false
  </code></pre>
  
  <p>For a collection model Month which has fields month(String), created_at, updated_at. However, <code>Month.where(month: /a/).include? 'January'</code> or <code>'Jan'</code> always returns false.</p>
  
  <p>Is there a similar method doing the same as Array.include? for Mongoid?, and how to use this 'include?' method?</p>