title: rails multiple checkboxes in 1 db column. saves correctly but doesn't show as checked
body: <p>Event saves the section id's in an array. But in the <code>/events/1/edit</code> view for a newly created event, the expected checkboxes are not checked. I'm guessing because the default for checkbox values is booleans.</p>
  
  <p><code>Event.last.newsletters #=&gt; ["108", "115", "116", "117", "118", ""]</code></p>
  
  <p>I have a CRUD for Event. Each Event can belong to multiple Sections. I have this displayed as a collection of checkboxes with the simpleform gem.</p>
  
  <pre><code>&lt;%= simple_form_for @event do |f| %&gt;
  ...
  &lt;%= f.collection_check_boxes :newsletters, Section.all, :id, :name, :input_html =&gt; { :class =&gt; 'checkbox' } %&gt;
  </code></pre>
  
  <p>This results in the following html:</p>
  
  <pre><code>&lt;span&gt;&lt;input id="event_newsletters_1" name="event[newsletters][]" type="checkbox" value="1" /&gt;&lt;label class="collection_check_boxes" for="event_newsletters_1"&gt;Newsletter 1&lt;/label&gt;&lt;/span&gt;
  &lt;span&gt;&lt;input id="event_newsletters_2" name="event[newsletters][]" type="checkbox" value="2" /&gt;&lt;label class="collection_check_boxes" for="event_newsletters_2"&gt;Newsletter 2&lt;/label&gt;&lt;/span&gt;
  etc. etc.
  </code></pre>
  
  <p>When I create a new event or edit an event, the newsletter values are saved properly in the model.</p>