trustieforge/app/models/system_message.rb

class SystemMessage < ActiveRecord::Base
  attr_accessible :content, :id, :user_id, :description, :subject
  belongs_to :user

  validates :subject, presence: true
  # validates :description, presence: true
  validates_length_of :description, maximum: 10000

  has_many :message_alls, :class_name => 'MessageAll',:as =>:message,  :dependent => :destroy
  acts_as_attachable

  # 系统消息放置总消息列表
  after_create :add_system_message

  def add_system_message
    if MessageAll.where("message_type = '#{self.class.to_s}' and message_id = '#{self.id}'").first.nil?
      self.message_alls << MessageAll.new(:user_id => self.user_id)
    end
  end
end