title: Ruby on Rails 4 - simple_form multiple select input
body: <p>I have a simple_form input field that looks like this:</p>
  
  <pre><code>&lt;%= f.input :particular_users, collection: @all_users, input_html: { class: 'multiselectuser', multiple: true} %&gt;
  </code></pre>
  
  <p>When I leave multiple: true off, the form submits the chosen value for the parameter :particular_users and I can see the value when debugging using "raise params.inspect". However when I leave the multiple: true option there, no vales get passed for the parameter :particular_users.</p>
  
  <p>What am I doing wrong?</p>
  
  <p><strong>EDIT:</strong> I can not use the association input because :particular_users is a virtual attribute  and has no relationship. I want the multiple select box to pass whatever values that are in there, even if they are arbitrary.</p>