Highlight changes being made on ActiveRecord object inside email

I simply needed one helper method which would help me highlight changes being made on any ActiveRecord object inside email. Below is one example of that I have come up with and would like to extend it in my future projects too.

It gave me some insights into ActiveRecord::Base#previous_changes and ActiveRecord::Base#reflections. Nice to learn such ActiveRecord features.

samg/diffy also helped me out decorating text changes

Adding to my MailerHelper

	module MailerHelper
	def highligh_changes_made_to object, options={}
	html = ""
	attrs = options[:attrs] || object.class.attribute_names
	html << "<br/><p>"
	attrs.each do |attr|
	html << "<p> #{attr.to_s.humanize} : "
	if object.previous_changes.include? attr.to_s
	if object.class.columns_hash[attr.to_s].type==:text
	html << "<br/>"
	html << text_changes(object.previous_changes[attr.to_s][0], object.previous_changes[attr.to_s][1])
	else
	html << "<font color='gray'>#{object_attr object, attr, object.previous_changes[attr.to_s][0]}</font> => "
	html << "<b>#{object_attr object, attr, object.previous_changes[attr.to_s][1]}</b>"
	end
	else
	html << "#{object_attr object, attr, (object.send attr.to_sym)}"
	end
	html << "</p>"
	end
	html << "<p/><br/>"
	html.html_safe
	end
	def object_attr object, attr, foreign_key_value
	return foreign_key_value unless attr.ends_with? "_id"
	assoc = object.class.reflections.values.select{ |assoc| assoc.foreign_key==attr }.first
	return "<NotFound>" unless assoc
	assoc.klass.where(:id => foreign_key_value).first || '""'
	end
	def text_changes str1, str2
	Diffy::Diff.new( str1, str2).collect do |line|
	case line
	when /^\+/ then
	"<b>#{line[1..-1]}</b>"
	when /^-/ then
	"<font color='gray'>#{line[1..-1]}</font>"
	when /^\// then
	else
	line
	end
	end.join("<br/>").to_s
	end
	end
	class ActionMailer::Base
	helper MailerHelper
	end

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mailer_helper.rb

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My rails mailer knows request and current_user

How about accessing @request and @current_user in your mailer

	# config/initializers/mailer_knows.rb
	module MailerBefore
	def before(hash)
	hash.keys.each do |key|
	define_method key.to_sym do
	eval " @#{key} = hash[key] "
	end
	end
	end
	end
	class ActionMailer::Base
	extend MailerBefore
	end
	class ActionController::Base
	before_filter :mailer_knows
	def mailer_knows
	ActionMailer::Base.before({
	:request => request,
	:current_user => (current_user and current_user.dup)
	})
	end
	end

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mailer_knows.rb

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