db/migrate/036_topics_cache_last_replied_user.rb

   1 class TopicsCacheLastRepliedUser < ActiveRecord::Migration
   2   class Post < ActiveRecord::Base; end
   3   class Topic < ActiveRecord::Base
   4     has_many :posts
   5   end
   6   def self.up
   7     add_column "topics", "replied_by", :integer
   8     add_column "topics", "last_post_id", :integer
   9     Topic.find(:all).each do |topic|
  10       next if topic.posts.count.zero?
  11       topic.replied_by   = topic.posts.last.user_id
  12       topic.last_post_id = topic.posts.last.id
  13       topic.save!
  14     end
  15   end
  16
  17   def self.down
  18     remove_column "topics", "replied_by"
  19     remove_column "topics", "last_post_id"
  20   end
  21 end