title: Django Rest Framework - Nested Serializer are lazy loaded?
body: <p>I am lovely using Django Rest Framework and have a lot of fun with it.
  But there is one thing which disturbes me. I have a Model and in this Model are a lot of Foreignkeys. i.e:</p>
  
  <pre><code>class Order(models.Model):
      bought_by = models.ForeignKey(User, related_name='bought_orders')
      bought_on = models.DateTimeField(default=datetime.datetime.now, blank=True)
      category = models.ForeignKey(OrderCategory, related_name='orders')
      article = models.ForeignKey(Article, related_name='orders')
      supplier = models.ForeignKey(Supplier, related_name='orders')
      purpose = models.CharField(null=True, blank=True, max_length=255)
      payment_method = models.ForeignKey(PaymentMethod, related_name='orders')
      order_number = models.CharField(max_length=255)
      delivery_received_on = models.DateTimeField(null=True, blank=True)
      delivery_received_by = models.ForeignKey(User, null=True, blank=True, related_name='received_orders')
      tags = TaggableManager(blank=True)
  </code></pre>
  
  <p>so I use the good ModelSerializer and by the way I use nested serializer i.e.:</p>
  
  <pre><code>class ReadOrderSerializer(ModelSerializer):
      created = DateTimeField()
      updated = DateTimeField()
      bought_by = UserSerializer()
      category = OrderCategorySerializer()
      article = ArticleSerializer()
      supplier = SupplierSerializer()
      payment_method = PaymentMethodSerializer()
      tags = TagListSerializerField()
      invoice_documents = InvoiceDocumentSerializer(many=True)
  </code></pre>
  
  <p>The problem is that the request takes about 1.7 seconds for only 50 order.
  Okay, that was unexpected... I opened my Django debug tool and looked at the sql statements. Django Rest Framework or Django opens for every order a new connection and do a select statement. </p>
  
  <p>Is there a possible way to walk around the problem? 
  Turn off lazy loading or something I can change in my serializers?</p>
  
  <p>Thank you very much!</p>