django1/tests/modeltests/defer/tests.py

from __future__ import absolute_import

from django.db.models.query_utils import DeferredAttribute
from django.test import TestCase

from .models import Secondary, Primary, Child, BigChild, ChildProxy


class DeferTests(TestCase):
    def assert_delayed(self, obj, num):
        count = 0
        for field in obj._meta.fields:
            if isinstance(obj.__class__.__dict__.get(field.attname),
                DeferredAttribute):
                count += 1
        self.assertEqual(count, num)

    def test_defer(self):
        # To all outward appearances, instances with deferred fields look the
        # same as normal instances when we examine attribute values. Therefore
        # we test for the number of deferred fields on returned instances (by
        # poking at the internals), as a way to observe what is going on.

        s1 = Secondary.objects.create(first="x1", second="y1")
        p1 = Primary.objects.create(name="p1", value="xx", related=s1)

        qs = Primary.objects.all()

        self.assert_delayed(qs.defer("name")[0], 1)
        self.assert_delayed(qs.only("name")[0], 2)
        self.assert_delayed(qs.defer("related__first")[0], 0)

        # Using 'pk' with only() should result in 3 deferred fields, namely all
        # of them except the model's primary key see #15494
        self.assert_delayed(qs.only("pk")[0], 3)

        obj = qs.select_related().only("related__first")[0]
        self.assert_delayed(obj, 2)

        self.assertEqual(obj.related_id, s1.pk)

        # You can use 'pk' with reverse foreign key lookups.
        self.assert_delayed(s1.primary_set.all().only('pk')[0], 3)

        self.assert_delayed(qs.defer("name").extra(select={"a": 1})[0], 1)
        self.assert_delayed(qs.extra(select={"a": 1}).defer("name")[0], 1)
        self.assert_delayed(qs.defer("name").defer("value")[0], 2)
        self.assert_delayed(qs.only("name").only("value")[0], 2)
        self.assert_delayed(qs.only("name").defer("value")[0], 2)
        self.assert_delayed(qs.only("name", "value").defer("value")[0], 2)
        self.assert_delayed(qs.defer("name").only("value")[0], 2)

        obj = qs.only()[0]
        self.assert_delayed(qs.defer(None)[0], 0)
        self.assert_delayed(qs.only("name").defer(None)[0], 0)

        # User values() won't defer anything (you get the full list of
        # dictionaries back), but it still works.
        self.assertEqual(qs.defer("name").values()[0], {
            "id": p1.id,
            "name": "p1",
            "value": "xx",
            "related_id": s1.id,
        })
        self.assertEqual(qs.only("name").values()[0], {
            "id": p1.id,
            "name": "p1",
            "value": "xx",
            "related_id": s1.id,
        })

        # Using defer() and only() with get() is also valid.
        self.assert_delayed(qs.defer("name").get(pk=p1.pk), 1)
        self.assert_delayed(qs.only("name").get(pk=p1.pk), 2)

        # DOES THIS WORK?
        self.assert_delayed(qs.only("name").select_related("related")[0], 1)
        self.assert_delayed(qs.defer("related").select_related("related")[0], 0)

        # Saving models with deferred fields is possible (but inefficient,
        # since every field has to be retrieved first).
        obj = Primary.objects.defer("value").get(name="p1")
        obj.name = "a new name"
        obj.save()
        self.assertQuerysetEqual(
            Primary.objects.all(), [
                "a new name",
            ],
            lambda p: p.name
        )

        # Regression for #10572 - A subclass with no extra fields can defer
        # fields from the base class
        Child.objects.create(name="c1", value="foo", related=s1)
        # You can defer a field on a baseclass when the subclass has no fields
        obj = Child.objects.defer("value").get(name="c1")
        self.assert_delayed(obj, 1)
        self.assertEqual(obj.name, "c1")
        self.assertEqual(obj.value, "foo")
        obj.name = "c2"
        obj.save()

        # You can retrive a single column on a base class with no fields
        obj = Child.objects.only("name").get(name="c2")
        self.assert_delayed(obj, 3)
        self.assertEqual(obj.name, "c2")
        self.assertEqual(obj.value, "foo")
        obj.name = "cc"
        obj.save()

        BigChild.objects.create(name="b1", value="foo", related=s1, other="bar")
        # You can defer a field on a baseclass
        obj = BigChild.objects.defer("value").get(name="b1")
        self.assert_delayed(obj, 1)
        self.assertEqual(obj.name, "b1")
        self.assertEqual(obj.value, "foo")
        self.assertEqual(obj.other, "bar")
        obj.name = "b2"
        obj.save()

        # You can defer a field on a subclass
        obj = BigChild.objects.defer("other").get(name="b2")
        self.assert_delayed(obj, 1)
        self.assertEqual(obj.name, "b2")
        self.assertEqual(obj.value, "foo")
        self.assertEqual(obj.other, "bar")
        obj.name = "b3"
        obj.save()

        # You can retrieve a single field on a baseclass
        obj = BigChild.objects.only("name").get(name="b3")
        self.assert_delayed(obj, 4)
        self.assertEqual(obj.name, "b3")
        self.assertEqual(obj.value, "foo")
        self.assertEqual(obj.other, "bar")
        obj.name = "b4"
        obj.save()

        # You can retrieve a single field on a baseclass
        obj = BigChild.objects.only("other").get(name="b4")
        self.assert_delayed(obj, 4)
        self.assertEqual(obj.name, "b4")
        self.assertEqual(obj.value, "foo")
        self.assertEqual(obj.other, "bar")
        obj.name = "bb"
        obj.save()

    def test_defer_proxy(self):
        """
        Ensure select_related together with only on a proxy model behaves
        as expected. See #17876.
        """
        related = Secondary.objects.create(first='x1', second='x2')
        ChildProxy.objects.create(name='p1', value='xx', related=related)
        children = ChildProxy.objects.all().select_related().only('id', 'name')
        self.assertEqual(len(children), 1)
        child = children[0]
        self.assert_delayed(child, 1)
        self.assertEqual(child.name, 'p1')
        self.assertEqual(child.value, 'xx')

    def test_defer_inheritance_pk_chaining(self):
        """
        When an inherited model is fetched from the DB, its PK is also fetched.
        When getting the PK of the parent model it is useful to use the already
        fetched parent model PK if it happens to be available. Tests that this
        is done.
        """
        s1 = Secondary.objects.create(first="x1", second="y1")
        bc = BigChild.objects.create(name="b1", value="foo", related=s1,
                                     other="bar")
        bc_deferred = BigChild.objects.only('name').get(pk=bc.pk)
        with self.assertNumQueries(0):
            bc_deferred.id
        self.assertEqual(bc_deferred.pk, bc_deferred.id)