_sidebar.html.erb

<div class="sidebar col-md-3">
  <div class="panel panel-default">
    <div class="panel-body">
      <a href="<%= new_note_path %>" class="btn btn-success btn-block">新建 Note</a>
    </div>
    <div class="panel-footer"><a href="<%= notes_path %>">查看我的 <%= current_user.notes.count %> 条 Note...</a></div>
  </div>

  <% if @recent_notes.present? %>
  <div class="panel panel-default">
    <div class="panel-heading">我最近创建的 Note</div>
    <ul class="list-group">
      <% @recent_notes.each do |note| %>
        <li class="list-group-item">
          <%= link_to note.display_title, note %>
        </li>
      <% end %>
    </ul>
  </div>
  <% end %>
</div>