title: Django Rest Framework - ForeignKey filtering in a serializer
body: <p>I have two models, <code>Fridge</code> and <code>Product</code>. <code>Fridge</code> has a ForeignKey to <code>auth.user</code>, while <code>Product</code> has a ForeignKey to <code>Fridge</code>, simple enough.</p>
  
  <p>Now quite obviously, I want an user to be able to add products only to his fridge. I want to create an API for that using DRF, AND I want a nice dropdown in the product viewset form, hence why I have to do this in a serializer. I'm using <code>viewsets.ViewSet</code> class, so <code>get_serializer_context</code> doesn't seem to have any effect.</p>
  
  <pre><code>class ProductSerializer(serializers.Serializer):
      pk = serializers.IntegerField(read_only=True)
      fridge = serializers.PrimaryKeyRelatedField(queryset=WHAT_QUERYSET)
      name = serializers.CharField(max_length=Product._meta.get_field('name').max_length)
      purchase_date = serializers.DateField()
      before_date = serializers.DateField()
  </code></pre>
  
  <p>I have no idea what should I put in the <code>queryset</code> keyword argument for the <code>fridge</code> attribute. I can't ask for <code>request.user</code> anywhere in that scope, as no context or request variables exist at that point. </p>