title: User has_many :users, :through => :friends - how?
body: <p>This is my code:</p>
  
  <pre><code>class Friend &lt; ActiveRecord::Base
    belongs_to :user
    belongs_to :friend, :class_name =&gt; "User", :foreign_key =&gt; "friend_id"
  end
  
  class User &lt; ActiveRecord::Base
    #...
    has_many :friends
    has_many :users, :through =&gt; :friends
    #...
  end
  </code></pre>
  
  <p>When I now start adding users by...</p>
  
  <pre><code>user.users &lt;&lt; user2
  user.save
  </code></pre>
  
  <p>Only the user_id of friend is filled, friend_id is null.</p>
  
  <p>Any help?</p>
  
  <p>Yours,
  Joern.</p>