title: Rails ActiveRecord: Select Posts WITHOUT comments
body: <p>I have a a Comments table and a Posts table, where a Post has many comments and a comment belongs to a post (i.e. it has a post_id in the table).</p>
  
  <p>How can I efficiently select the last ten Posts that DO NOT have comments.
  I can't seem to accomplish this without first selecting all the posts and checking each for a 0 comment count.</p>
  
  <p>Thanks in advance for any help.</p>
  
  <p>-Nathan</p>