If you get one of these errors, it's highly likely that you've upgraded to Rails 2.2 or higher:

undefined method white_list_sanitizer' for String:Class
undefined method full_sanitizer' for String:Class

The fix is to extend the SanitizeHelper.

class String
  extend ActionView::Helpers::SanitizeHelper::ClassMethods
end

Thinking about escaping and sanitizing input and output? Read this: https://security.stackexchange.com/questions/95325/input-sanitization-vs-output-sanitization

Rules:

• Always sanitize output

By sanitizing the output, you can fix issues caused by bugs in the input sanitizer without touching the database.

• Sanitize input, if it makes sense:

For example, if there’s a risk that input becomes invalid after sanitization then it’s better to store the data raw.

This is also a good idea, if there are multiple output formats and sanitizing the input might break something.