contrived migration

migration.rb

class UpdatePosts < ActiveRecord::Migration
  class Post < ActiveRecord::Base
    has_many :comments
  end
  
  class Comment < ActiveRecord::Base
    belongs_to :post
  end
  
  def change
    add_column :comments, :provider, :string
    
    #updates comment provider
    Post.where("created_at > :boundary", boundary: 7.months.ago).find_each do |post|
      post.comments.find_each do |comment|
        comment.provider = 'disqus'
        comment.save!
      end
    end
  end
end