ask/app/views/admin/asks/print_setting.html.erb

<div>
  <form>
    <h4><%= t(:category) %></h4>
    <select name="category" id="submit_when_change">
      <% @cats_relations.each do |id, title| %>
        <option value="<%=id%>" <%= @category_id == id ? 'selected' : '' %>><%= title %></option>
      <% end %>
    </select>
  </form>
</div>
<%= form_for @set, as: :ask_print_setting ,method: 'post',url:  @url,html: { class: 'form-horizontal main-forms previewable' } do |f| %>
  <%= hidden_field_tag "#{f.object_name}[category_id]", @category_id %>
  <fieldset>
    <table>
      <thead>
        <tr>
          <th></th>
          <th></th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <td>
            <%= label_tag t('ask.save_name') %>
          </td>
          <td>
            <%= f.text_field :save_name %>
          </td>
        </tr>
        <tr>
          <td>
            <%= label_tag t('ask.print_format') %>
          </td>
          <td>
            <%= f.text_area :print_format,class: 'ckeditor' %>
          </td>
        </tr>
        <tr>
          <td colspan="2" style="text-align: center;">
            <input class="btn btn-primary" type="submit" value="<%= t('submit')%>">
          </td>
        </tr>
      </tbody>
    </table>
  </fieldset>
<% end %>
<%= render partial: 'print_format_explain' %>
<script>
  $(document).ready(function(){
    $("#submit_when_change").on("change",function(){
      $(this)[0].form.submit();
    })
  })
</script>