title: Django - Filter queryset with child objects (ForeignKey)
body: <p>I have 3 Models, and 2 of them correspond to the first one.</p>
  
  <pre><code>class Parent(models.Model):
      name = models.CharField....
      ...
  
  class Child1(models.Model):
     parent = models.ForeignKey(Parent)
     ...
  
  class Child2(models.Model):
     parent = models.ForeignKey(Parent)
     ...
  </code></pre>
  
  <p>Now, in my view I have 2 querysets filtered of <code>Child1</code> and <code>Child2</code> objects.</p>
  
  <p>Is there a way to retrieve all the <code>Parent</code> objects that are in the filtered querysets?</p>
  
  <p>Something like...</p>
  
  <pre><code>children1 = Child1.objects.filter(blah=blah)
  children2 = Child2.objects.filter(blah=blah)
  parents = Parent.objects.filter(self__in=children1 or self__in=children2)
  </code></pre>
  
  <p><strong>NOTE</strong> The code above does not works at all, it is just the idea.</p>