app/views/shared/_validation.html.erb
<% if object.errors.any? %>
<div class="alert alert-danger alert-dismissible" role="alert">
<button type="button" class="close" data-dismiss="alert" aria-label="Close"><span aria-hidden="true">×</span></button>
<strong>The form contains </strong> <%= pluralize(object.errors.count, "error") %> .
<ul class="list-group">
<% object.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>