title: Conditional scope on parent association to get all children
body: <p>I want to fetch all the comments whom articles are published. So what scope definition will give me the results.
  In articles model</p>
  
  <pre><code>has_many :comments
  </code></pre>
  
  <p>Comment model</p>
  
  <pre><code>belongs_to :article
  </code></pre>