title: eloquent search/where on custom attributes
body: <p>I added a custom attribute to my model</p>
  
  <pre><code>public function getTouchedAttribute() { ...
  </code></pre>
  
  <p>I would like to add this to a query </p>
  
  <pre><code>hasMany()-&gt;where('touched', ...)
  </code></pre>
  
  <p>but obviously this isn't a column in the table. </p>
  
  <p>what is the most elegant way to achieve this behavior?</p>