ActiveRecord macro example

polite.rb

require "active_record"

module Polite
  BAD_WORDS = ["fuck", "asshole", "motherfucker", "cunt", "cock", "dickhead"]
  ESCAPED = BAD_WORDS.collect {|word| Regexp.escape(word)}
  RE = /(#{ESCAPED.join("|")})/i

  def self.extended(base)
    base.extend ClassMethods
  end
end

module Polite
  module ClassMethods
    def be_polite(*names)
      before_save :remove_bad_words_from_attributes

      cattr_accessor :polite_attributes
      self.polite_attributes = names

      include InstanceMethods
    end
  end
end

module Polite
  module InstanceMethods
    private
    def remove_bad_words_from_attributes
      self.class.polite_attributes.each do |attribute|
        remove_bad_words_from(attribute)
      end
    end

    def remove_bad_words_from(attribute)
      value = send(attribute).to_s.gsub(RE) { $1[0,1] << "*" }
      send("#{attribute}=", value)
    end
  end
end

# Extend ActiveRecord
ActiveRecord::Base.extend(Polite)

# Establish connection
ActiveRecord::Base.establish_connection(:adapter => "sqlite3", :database => ":memory:")

# Create a demo table
ActiveRecord::Schema.define(:version => 0) do
  create_table :comments do |t|
    t.text :body
  end
end

# Create a demo model
class Comment < ActiveRecord::Base
  be_polite :body
end

comment = Comment.create(:body => "Fuck you, asshole!")
p comment.body
#=> "F* you, a*!"