title: select_related queryset with ModelSerializer in Django rest framework
body: <p>I'm trying to use the "select_related" queryset method with DRF serializers, 
  but this example is still doing a lot of sql queries.</p>
  
  <p>How can I get the related object "model_b" from select_related method?  </p>
  
  <pre><code>class Model_A(models.Model):
      title = models.CharField(max_length=100)
      description = models.TextField()
      model_b = models.ForeignKey(Model_B, null=True, blank=True)
  
  class Model_B(models.Model):
      title = models.CharField(max_length=100)
  
  
  class Model_A_Serializer(serializers.ModelSerializer):
      model_b = Model_B_Serializer(source="model_b")
      class Meta:
          model = Model_A
          fields = ('title', 'model_b')
  
  class Model_B_Serializer(serializers.ModelSerializer):
      class Meta:
          model = Model_B
  
  
  class Model_A_View(viewsets.ModelViewSet):
      serializer_class = Model_A_Serializer
      queryset = Model_A.objects.select_related('model_b').all()
  </code></pre>