class HomeworkCommonTime < ActiveRecord::Migration
  def up
    count = StudentWork.all.count / 100 + 1
    transaction do
      for i in 1 ... count do i
      StudentWork.page(i).per(100).each do |homework|
        old_homework = HomeworkAttach.where(:user_id => homework.user_id, :name => homework.name, :description => homework.description).first
        if old_homework
          homework.update_column('created_at', old_homework.created_at)
        end
      end
      end
    end
  end

  def down
  end
end