title: Rails 3 - how to save (un)checked checkboxes?
body: <p>I have in a form (<strong>form_tag</strong>) several checkboxes like this:</p>
  
  <pre><code>&lt;%=check_box_tag 'model_name[column_name]', 1, (@data.model_name.column_name == 1 ? true : false)%&gt;
  </code></pre>
  
  <p>And updating them like:</p>
  
  <pre><code>variable = ModelName.find(params[:id])             
  variable.update_attributes(params[:model_name])
  </code></pre>
  
  <p>This works only in a moment, when I check some checkboxes - send them and they will be saved. That's fine.
  But when I uncheck all checkboxes - send form - so nothing happend, in the DB table will not set the value <strong>0</strong> in the columns...</p>
  
  <p>Could you give me any tip, how to fix it? </p>
  
  <p>Thank you in advance</p>