title: Laravel Eloquent, select only rows where the relation exists
body: <p>I am trying to select from a table, but I only want to select things that have an existing relationship.</p>
  
  <p>For example, if I have Users and Comments, and Users haveMany Comments, I want to do something like:</p>
  
  <pre><code>User::hasComments()-&gt;paginate(20);
  </code></pre>
  
  <p>So, I only want to select Users that have at least 1 Comment, and paginate the result of that query. Is there any way to do this?</p>