gistfile1.rb

class AddCommentsCountToArticles < ActiveRecord::Migration
  def up
    add_column :articles, :comments_count, :integer, null: false, default: 0
    Article.reset_column_information
    ids = Set.new
    Article.all.each {|art| ids << art.id}
    ids.each do |article_id|
      Article.reset_counters(article_id, :comments)
    end
  end

  def down
    remove_column :articles, :comments_count
  end
end