title: Mutator for unique user attribute
body: <p>In my code the line <code>User::where('socialite_id', $socialite_id)-&gt;exists();</code> is used so many times, that i want to just write a mutator or sth around it to make this line shorter.</p>
  <p>So i need to make mutator, that checks if there's a user with the same <code>socialite_id</code> that a new user is about to have.</p>
  <p>I've come with</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>    public function hasUniqueSocialiteIdAttribute($value){
          return !$this-&gt;where('socialite_id', $value)-&gt;exists();
      }</code></pre>
  </div>
  </div>
  </p>
  <p>Mabye it is better to catch the duplicate exception and abort on catch, but.. naah.</p>
  <p>But this thing is not working. Any suggestions?</p>