class MigrateStudentWorks < ActiveRecord::Migration
  def up
    count = Course.all.count / 30 + 2
    transaction do
      for i in 1 ... count do i
        Course.page(i).per(30).each do |course|
          homework_ids = course.homework_commons.blank? ? "(-1)" : "(" + course.homework_commons.map{|hw| hw.id}.join(",") + ")"
          student_ids = course.student.blank? ? "(-1)" : "(" + course.student.map{|st| st.student_id}.join(",") + ")"
          student_works = StudentWork.where("homework_common_id in #{homework_ids} and user_id not in #{student_ids}")
          student_works.update_all(:is_delete => 1)
        end
      end
    end
  end

  def down
  end
end