socialforge/app/models/course_activity.rb

class CourseActivity < ActiveRecord::Base
  attr_accessible :user_id, :course_act_id,:course_act_type,:course_id
  # 虚拟关联
  belongs_to :course_act ,:polymorphic => true
  belongs_to :course
  belongs_to :user
  has_many :user_acts, :class_name => 'UserAcivity',:as =>:act
  after_save :add_user_activity
  before_destroy :destroy_user_activity

  #在个人动态里面增加当前动态
  def add_user_activity
    user_activity = UserActivity.where("act_type = '#{self.class.to_s}' and act_id = '#{self.id}'").first
    if user_activity
      user_activity.save
    else
      user_activity = UserActivity.new
      user_activity.act_id = self.id
      user_activity.act_type = self.class.to_s
      user_activity.container_type = "Course"
      user_activity.container_id = self.course_id
      user_activity.save
    end
  end

  def destroy_user_activity
    user_activity = UserActivity.where("act_type = '#{self.class.to_s}' and act_id = '#{self.id}'")
    user_activity.destroy_all
  end
end