class DeleteNullCourseActivity < ActiveRecord::Migration
  def up
    count = CourseActivity.all.count / 30 + 2
    transaction do
      for i in 1 ... count do i
        CourseActivity.page(i).per(30).each do |activity|
          unless activity.course_act
            activity.destroy
          end
        end
      end
    end
  end

  def down
  end
end