Cacher is the code snippet organizer for pro developers

class AddCommentsCountToPosts < ActiveRecord::Migration
  def change
    change_table :posts do |t|
      t.integer :comments_count, default: 0
    end

    reversible do |dir|
      dir.up { fast }
    end
  end

  # DO THIS!
  def fast
    execute <<-SQL.squish
        UPDATE posts
           SET comments_count = (SELECT count(1)
                                   FROM comments
                                  WHERE comments.post_id = posts.id);
    SQL
  end
 
  # NOT THIS! 
  def slow
    Post.reset_column_information
    say_with_time "Seeding posts.comments_count -- Better grab a coffee." do
      print "   -> "
      Post.select(:id).find_in_batches do |posts|
        print "."
        posts.each do |s|
          Post.reset_counters s.id, :comments
        end
      end
      puts
      Post.count
    end
  end
end