Improve form fields with errors for model updates

config/initializers/field_with_errors.rb

@@ -0,0 +1,9 @@
+ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
+  if html_tag.match('class')
+    html_tag.gsub(/class="(.*?)"/, 'class="\1 field_with_errors"').html_safe
+  else
+    parts = html_tag.split('>', 2)
+    parts[0] += ' class="field_with_errors">'
+    (parts[0] + parts[1]).html_safe
+  end
+end