title: Django combine foreign keys in a single queryset
body: <p>I have a model in a Django application that is being referenced by multiple other models as a ForeignKey.</p>
  
  <p>What I am looking for is for a way to create a <strong>single queryset</strong> for all objects of this class that are being referenced as ForeignKey by the rest of the classes based on some criteria.</p>
  
  <p>I am not even sure if this is possible, but I thought about asking anyway.</p>
  
  <pre><code>class Person(models.Model):
      pass
  
  
  class Book(models.Model):
      year_published = models.PositiveIntegerField()
      author = models.ForeignKey(Person)
  
  
  class MusicAlbum(models.Model):
      year_published = models.PositiveIntegerField()
      producer = models.ForeignKey(Person)
  
  recent_books = Book.objects.filter(year_published__gte=2018)
  recent_music_albums = MusicAlbum.objects.filter(year_published__gte=2018)
  
  # How can I create a **single** queryset of the Person objects that are being referenced as `author` in `recent_books` and as `producer` in `recent_music_albums`?
  </code></pre>
  
  <p>Thanks for your time.</p>