socialforge/app/models/students_for_course.rb

class StudentsForCourse < ActiveRecord::Base
  attr_accessible :course_id, :student_id
  
  belongs_to :course, :class_name => 'Course', :foreign_key => :course_id

  belongs_to :student, :class_name => 'User', :foreign_key => :student_id
  
  validates_presence_of :course_id, :student_id
  validates_uniqueness_of :student_id, :scope => :course_id

  after_destroy :delete_student_works
  after_create :recovery_student_works

  #退出班级或删除学生时隐藏学生的作品
  def delete_student_works
    course = self.course
    homework_ids = course.homework_commons.blank? ? "(-1)" : "(" + course.homework_commons.map{|hw| hw.id}.join(",") + ")"
    student_works = StudentWork.where("user_id = #{self.student_id} && homework_common_id in #{homework_ids}")
    student_works.update_all(:is_delete => 1)
  end

  #加入班级时还原作品
  def recovery_student_works
    course = self.course
    homework_ids = course.homework_commons.blank? ? "(-1)" : "(" + course.homework_commons.map{|hw| hw.id}.join(",") + ")"
    student_works = StudentWork.where("user_id = #{self.student_id} && homework_common_id in #{homework_ids}")
    student_works.update_all(:is_delete => 0)
  end
end