title: Pre-checking collection of model objects used as check boxes with Formtastic
body: <p>So I've got some objects that I'm passing as a collection:</p>
  
  <pre><code>@things = Thing.all
  </code></pre>
  
  <p>And in my view:</p>
  
  <pre><code>&lt;%= f.input :things, :collection =&gt; @things, :as =&gt; :check_boxes %&gt;
  </code></pre>
  
  <p>Is there any way to specify which of the objects should already be checked when the view is loaded?</p>
  
  <p>Thanks!</p>