cleaner.rb

module AttrCleaner
  module ModuleMixin
    def self.included(base)
      base.class_eval do
        extend ClassMethods
        alias_method_chain :write_attribute, :cleaner
      end
    end
    
    module ClassMethods
      @@attr_cleaners = []
      
      def write_attribute_with_cleaner(attr_name, value)
        if @@attr_cleaners.include?(attr_name.to_sym) && value.is_a?(String)
          # Don't modify in place since we don't control it's origin.
          value = value.strip
          value = nil if value.empty?
        end
        write_attribute_without_cleaner(attr_name, value)
      end
      
      def attr_cleaner(*args)
        only = Array(args[:only])
        except = Array(args[:except])
        
        columns = column_names.map(&:to_sym) & only
        
        @@attr_cleaners = columns - except
      end        
    end
  end
end