title: Rails. Simple form multipart file not working
body: <p>I use simple_form and multipart uploading does not work(uploading a single file works). Rails file_field_tag work...<br>
  Rails 3.2.13</p>
  
  <pre><code>&lt;%= simple_form_for @building, input_html: {multipart: true} do |f| %&gt;
  ...
  
    &lt;%= f.simple_fields_for :paintings do |p| %&gt;
      &lt;%= p.input :image, as: :file %&gt;
    &lt;% end %&gt;
  
  &lt;% end %&gt;
  </code></pre>