title: Trying To Define a Relationship With Two Possible Foreign Keys
body: <p>I am using the Spatie Activitylog extension in Laravel 8 in a project to track funnily enough activities within the site. Within the activity model there are two polymorphic relationships defined as causer and subject. In my user model I am trying to create a relationship which will return all related activity models where the user is in either the causer or subject polymorphic fields.</p>
  <p>The two relationships I have in there so far are...</p>
  <pre><code>public function activitiesOn(): MorphMany {
        return $this-&gt;morphMany(App\Model\Activity, 'subject');
    }
  
  
  public function activitiesBy(): MorphMany {
      return $this-&gt;morphMany(App\Model\Activity, 'causer');
  }
  </code></pre>
  <p>But I am struggling to figure out a way to get activities returned by both those relationships to show up as a single entry in the returned model under <code>activities</code>.</p>