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from django.db.models.query_utils import DeferredAttribute
from django.test import TestCase
from models import Secondary, Primary, Child, BigChild
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)
obj = qs.select_related().only("related__first")[0]
self.assert_delayed(obj, 2)
self.assertEqual(obj.related_id, s1.pk)
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()
|
