title: dependent => destroy on a "has_many through" association
body: <p>Apparently dependent => destroy is ignored when also using the :through option.</p>
  
  <p>So I have this...</p>
  
  <pre><code>class Comment &lt; ActiveRecord::Base
    has_many :comment_users, :dependent =&gt; :destroy
    has_many :users, :through =&gt; :comment_users
    ...
  end
  </code></pre>
  
  <p>...but deleting a Comment does not result in the associated comment_user records getting deleted.</p>
  
  <p>What's the recommended approach, then, for cascade deletes when using :through?</p>
  
  <p>Thanks</p>