Avoided creation of deferred model from another deferred model

    being replaced with DeferredAttribute objects. The "pk_value" ties the

    deferred attributes to a particular instance of the model.

    """

    if not attrs:

        return model

    # Never create deferred models based on deferred model

    if model._deferred:

        # Deferred models are proxies for the non-deferred model. We never

        # create chains of defers => proxy_for_model is the non-deferred

        # model.

        model = model._meta.proxy_for_model

    # The app registry wants a unique name for each model, otherwise the new

    # class won't be created (we get an exception). Therefore, we generate

    # the name using the passed in attrs. It's OK to reuse an existing class

from django.contrib.contenttypes.models import ContentType

from django.contrib.sessions.backends.db import SessionStore

from django.db.models import Count

from django.db.models.query_utils import deferred_class_factory, DeferredAttribute

from django.test import TestCase, override_settings

from .models import (

        self.assertEqual(len(qs), 1)

    def test_deferred_class_factory(self):

        from django.db.models.query_utils import deferred_class_factory

        new_class = deferred_class_factory(

            Item,

            ('this_is_some_very_long_attribute_name_so_modelname_truncation_is_triggered',))

            new_class.__name__,

            'Item_Deferred_this_is_some_very_long_attribute_nac34b1f495507dad6b02e2cb235c875e')

    def test_deferred_class_factory_already_deferred(self):

        deferred_item1 = deferred_class_factory(Item, ('name',))

        deferred_item2 = deferred_class_factory(deferred_item1, ('value',))

        self.assertIs(deferred_item2._meta.proxy_for_model, Item)

        self.assertFalse(isinstance(deferred_item2.__dict__.get('name'), DeferredAttribute))

        self.assertTrue(isinstance(deferred_item2.__dict__.get('value'), DeferredAttribute))

    def test_deferred_class_factory_no_attrs(self):

        deferred_cls = deferred_class_factory(Item, ())

        self.assertFalse(deferred_cls._deferred)

class DeferAnnotateSelectRelatedTest(TestCase):

    def test_defer_annotate_select_related(self):