title: Polymorphic, get user liked activities
body: <p>I have a polymorphic one-to-many realtionship defined between Activity and Like.
  A User can like the activity but<br>
  how can I get all activities liked by a user?</p>
  
  <pre><code>class Activity extends Model
  {   
      public function likes(){
          return $this-&gt;morphMany('App\Like', 'likeable');
      }
  
      public function like($user = 0){
          $this-&gt;likes()-&gt;updateOrCreate([
              'user_id' =&gt; $user ? $user-&gt;id : Auth::id(),
          ], [
              'liked' =&gt; true
          ]);
      }
  }
  </code></pre>
  
  <pre><code>class Like extends Model
  {
      public function likeable(){
          return $this-&gt;morphTo();
      }
  }
  </code></pre>
  
  <pre><code>class User extends Authenticatable
  {
      public function likes(){
          // Get all liked activities by a user.
      }
  }
  </code></pre>