title: Creating Association between mongodb and active record
body: <p>How can I create association like has_many, has_and_belongs_to_many, belongs_to between mongodb models and active record models for example. I have a class <code>Item</code> which is  using mongoid and I have another class <code>ItemType</code> that inherits from <code>ActiveRecord</code></p>
  
  <pre><code>class Item
    include Mongoid::Document
    embeds_many :extra_fields, class_name: "ItemType"
  end
  
  class ItemType &lt; ActiveRecord::Base
    belongs_to :item
  end
  </code></pre>
  
  <p>Thanks</p>