polymphic, comment,db

use polymphic 's benefit
would not need the new table, just change the type could be used for the new model

如果model的相似度高例如 comment , 一個網站裡面很多都可以需要comment

就可以用這個

[forum model]
  has_many :comments, :as => :record

[record model]
  has_many :comments, :as => :record

[comment model]
  belongs_to :record, :polymorphic => true

[comments table]
  create_table "comments", :force => true do |t|
    t.text     "content"
    t.integer  "record_id",   :limit => 11, :null => false
    t.string   "record_type"
  end