Helper pour modifier un field de form quand il y a un erreur

form.html.erb

<% field_with_errors @zonage, :name do %>
<div class="control-group">
  <%= f.label 'Nom du zonage', :class => 'control-label' %>
  <div class="controls">
    <%= f.text_field :name %>
  </div>
</div>
<% end %>

helper.rb

# http://lukecarrier.me/2011/08/rails-3-0-select-tags-and-field_with_errors/
# modified for replacer a class
def field_with_errors(object, method, &block)
  if block_given?
    if object.errors[method].empty?
      concat capture(&block)
    else
      add_error = capture(&block).gsub("control-group", "control-group error")
      concat raw(add_error)
    end
  end
end