django/tests/basic/tests.py

from __future__ import unicode_literals

from datetime import datetime, timedelta
import threading
import warnings

from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
from django.db import connections, DEFAULT_DB_ALIAS
from django.db import DatabaseError
from django.db.models.fields import Field
from django.db.models.fields.related import ForeignObjectRel
from django.db.models.manager import BaseManager
from django.db.models.query import QuerySet, EmptyQuerySet
from django.test import TestCase, TransactionTestCase, skipIfDBFeature, skipUnlessDBFeature
from django.utils import six
from django.utils.translation import ugettext_lazy

from .models import Article, SelfRef, ArticleSelectOnSave


class ModelInstanceCreationTests(TestCase):

    def test_object_is_not_written_to_database_until_save_was_called(self):
        a = Article(
            id=None,
            headline='Area man programs in Python',
            pub_date=datetime(2005, 7, 28),
        )
        self.assertIsNone(a.id)
        self.assertEqual(Article.objects.all().count(), 0)

        # Save it into the database. You have to call save() explicitly.
        a.save()
        self.assertIsNotNone(a.id)
        self.assertEqual(Article.objects.all().count(), 1)

    def test_can_initialize_model_instance_using_positional_arguments(self):
        """
        You can initialize a model instance using positional arguments,
        which should match the field order as defined in the model.
        """
        a = Article(None, 'Second article', datetime(2005, 7, 29))
        a.save()

        self.assertEqual(a.headline, 'Second article')
        self.assertEqual(a.pub_date, datetime(2005, 7, 29, 0, 0))

    def test_can_create_instance_using_kwargs(self):
        a = Article(
            id=None,
            headline='Third article',
            pub_date=datetime(2005, 7, 30),
        )
        a.save()
        self.assertEqual(a.headline, 'Third article')
        self.assertEqual(a.pub_date, datetime(2005, 7, 30, 0, 0))

    def test_autofields_generate_different_values_for_each_instance(self):
        a1 = Article.objects.create(headline='First', pub_date=datetime(2005, 7, 30, 0, 0))
        a2 = Article.objects.create(headline='First', pub_date=datetime(2005, 7, 30, 0, 0))
        a3 = Article.objects.create(headline='First', pub_date=datetime(2005, 7, 30, 0, 0))
        self.assertNotEqual(a3.id, a1.id)
        self.assertNotEqual(a3.id, a2.id)

    def test_can_mix_and_match_position_and_kwargs(self):
        # You can also mix and match position and keyword arguments, but
        # be sure not to duplicate field information.
        a = Article(None, 'Fourth article', pub_date=datetime(2005, 7, 31))
        a.save()
        self.assertEqual(a.headline, 'Fourth article')

    def test_cannot_create_instance_with_invalid_kwargs(self):
        six.assertRaisesRegex(
            self,
            TypeError,
            "'foo' is an invalid keyword argument for this function",
            Article,
            id=None,
            headline='Some headline',
            pub_date=datetime(2005, 7, 31),
            foo='bar',
        )

    def test_can_leave_off_value_for_autofield_and_it_gets_value_on_save(self):
        """
        You can leave off the value for an AutoField when creating an
        object, because it'll get filled in automatically when you save().
        """
        a = Article(headline='Article 5', pub_date=datetime(2005, 7, 31))
        a.save()
        self.assertEqual(a.headline, 'Article 5')
        self.assertNotEqual(a.id, None)

    def test_leaving_off_a_field_with_default_set_the_default_will_be_saved(self):
        a = Article(pub_date=datetime(2005, 7, 31))
        a.save()
        self.assertEqual(a.headline, 'Default headline')

    def test_for_datetimefields_saves_as_much_precision_as_was_given(self):
        """as much precision in *seconds*"""
        a1 = Article(
            headline='Article 7',
            pub_date=datetime(2005, 7, 31, 12, 30),
        )
        a1.save()
        self.assertEqual(Article.objects.get(id__exact=a1.id).pub_date,
            datetime(2005, 7, 31, 12, 30))

        a2 = Article(
            headline='Article 8',
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        a2.save()
        self.assertEqual(Article.objects.get(id__exact=a2.id).pub_date,
            datetime(2005, 7, 31, 12, 30, 45))

    def test_saving_an_object_again_does_not_create_a_new_object(self):
        a = Article(headline='original', pub_date=datetime(2014, 5, 16))
        a.save()
        current_id = a.id

        a.save()
        self.assertEqual(a.id, current_id)

        a.headline = 'Updated headline'
        a.save()
        self.assertEqual(a.id, current_id)

    def test_querysets_checking_for_membership(self):
        headlines = [
            'Area man programs in Python', 'Second article', 'Third article']
        some_pub_date = datetime(2014, 5, 16, 12, 1)
        for headline in headlines:
            Article(headline=headline, pub_date=some_pub_date).save()
        a = Article(headline='Some headline', pub_date=some_pub_date)
        a.save()

        # You can use 'in' to test for membership...
        self.assertIn(a, Article.objects.all())
        # ... but there will often be more efficient ways if that is all you need:
        self.assertTrue(Article.objects.filter(id=a.id).exists())


class ModelTest(TestCase):
    def test_objects_attribute_is_only_available_on_the_class_itself(self):
        six.assertRaisesRegex(
            self,
            AttributeError,
            "Manager isn't accessible via Article instances",
            getattr,
            Article(),
            "objects",
        )
        self.assertFalse(hasattr(Article(), 'objects'))
        self.assertTrue(hasattr(Article, 'objects'))

    def test_queryset_delete_removes_all_items_in_that_queryset(self):
        headlines = [
            'An article', 'Article One', 'Amazing article', 'Boring article']
        some_pub_date = datetime(2014, 5, 16, 12, 1)
        for headline in headlines:
            Article(headline=headline, pub_date=some_pub_date).save()
        self.assertQuerysetEqual(Article.objects.all().order_by('headline'),
            ["<Article: Amazing article>",
             "<Article: An article>",
             "<Article: Article One>",
             "<Article: Boring article>"])
        Article.objects.filter(headline__startswith='A').delete()
        self.assertQuerysetEqual(Article.objects.all().order_by('headline'),
            ["<Article: Boring article>"])

    def test_not_equal_and_equal_operators_behave_as_expected_on_instances(self):
        some_pub_date = datetime(2014, 5, 16, 12, 1)
        a1 = Article.objects.create(headline='First', pub_date=some_pub_date)
        a2 = Article.objects.create(headline='Second', pub_date=some_pub_date)
        self.assertNotEqual(a1, a2)
        self.assertEqual(a1, Article.objects.get(id__exact=a1.id))

        self.assertNotEqual(Article.objects.get(id__exact=a1.id), Article.objects.get(id__exact=a2.id))

    @skipUnlessDBFeature('supports_microsecond_precision')
    def test_microsecond_precision(self):
        # In PostgreSQL, microsecond-level precision is available.
        a9 = Article(
            headline='Article 9',
            pub_date=datetime(2005, 7, 31, 12, 30, 45, 180),
        )
        a9.save()
        self.assertEqual(Article.objects.get(pk=a9.pk).pub_date,
            datetime(2005, 7, 31, 12, 30, 45, 180))

    @skipIfDBFeature('supports_microsecond_precision')
    def test_microsecond_precision_not_supported(self):
        # In MySQL, microsecond-level precision isn't available. You'll lose
        # microsecond-level precision once the data is saved.
        a9 = Article(
            headline='Article 9',
            pub_date=datetime(2005, 7, 31, 12, 30, 45, 180),
        )
        a9.save()
        self.assertEqual(Article.objects.get(id__exact=a9.id).pub_date,
            datetime(2005, 7, 31, 12, 30, 45))

    def test_manually_specify_primary_key(self):
        # You can manually specify the primary key when creating a new object.
        a101 = Article(
            id=101,
            headline='Article 101',
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        a101.save()
        a101 = Article.objects.get(pk=101)
        self.assertEqual(a101.headline, 'Article 101')

    def test_create_method(self):
        # You can create saved objects in a single step
        a10 = Article.objects.create(
            headline="Article 10",
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        self.assertEqual(Article.objects.get(headline="Article 10"), a10)

    def test_year_lookup_edge_case(self):
        # Edge-case test: A year lookup should retrieve all objects in
        # the given year, including Jan. 1 and Dec. 31.
        Article.objects.create(
            headline='Article 11',
            pub_date=datetime(2008, 1, 1),
        )
        Article.objects.create(
            headline='Article 12',
            pub_date=datetime(2008, 12, 31, 23, 59, 59, 999999),
        )
        self.assertQuerysetEqual(Article.objects.filter(pub_date__year=2008),
            ["<Article: Article 11>", "<Article: Article 12>"])

    def test_unicode_data(self):
        # Unicode data works, too.
        a = Article(
            headline='\u6797\u539f \u3081\u3050\u307f',
            pub_date=datetime(2005, 7, 28),
        )
        a.save()
        self.assertEqual(Article.objects.get(pk=a.id).headline,
            '\u6797\u539f \u3081\u3050\u307f')

    def test_hash_function(self):
        # Model instances have a hash function, so they can be used in sets
        # or as dictionary keys. Two models compare as equal if their primary
        # keys are equal.
        a10 = Article.objects.create(
            headline="Article 10",
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        a11 = Article.objects.create(
            headline='Article 11',
            pub_date=datetime(2008, 1, 1),
        )
        a12 = Article.objects.create(
            headline='Article 12',
            pub_date=datetime(2008, 12, 31, 23, 59, 59, 999999),
        )

        s = {a10, a11, a12}
        self.assertIn(Article.objects.get(headline='Article 11'), s)

    def test_field_ordering(self):
        """
        Field instances have a `__lt__` comparison function to define an
        ordering based on their creation. Prior to #17851 this ordering
        comparison relied on the now unsupported `__cmp__` and was assuming
        compared objects were both Field instances raising `AttributeError`
        when it should have returned `NotImplemented`.
        """
        f1 = Field()
        f2 = Field(auto_created=True)
        f3 = Field()
        self.assertLess(f2, f1)
        self.assertGreater(f3, f1)
        self.assertIsNotNone(f1)
        self.assertNotIn(f2, (None, 1, ''))

    def test_extra_method_select_argument_with_dashes_and_values(self):
        # The 'select' argument to extra() supports names with dashes in
        # them, as long as you use values().
        Article.objects.create(
            headline="Article 10",
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        Article.objects.create(
            headline='Article 11',
            pub_date=datetime(2008, 1, 1),
        )
        Article.objects.create(
            headline='Article 12',
            pub_date=datetime(2008, 12, 31, 23, 59, 59, 999999),
        )

        dicts = Article.objects.filter(
            pub_date__year=2008).extra(
            select={'dashed-value': '1'}).values('headline', 'dashed-value')
        self.assertEqual([sorted(d.items()) for d in dicts],
            [[('dashed-value', 1), ('headline', 'Article 11')], [('dashed-value', 1), ('headline', 'Article 12')]])

    def test_extra_method_select_argument_with_dashes(self):
        # If you use 'select' with extra() and names containing dashes on a
        # query that's *not* a values() query, those extra 'select' values
        # will silently be ignored.
        Article.objects.create(
            headline="Article 10",
            pub_date=datetime(2005, 7, 31, 12, 30, 45),
        )
        Article.objects.create(
            headline='Article 11',
            pub_date=datetime(2008, 1, 1),
        )
        Article.objects.create(
            headline='Article 12',
            pub_date=datetime(2008, 12, 31, 23, 59, 59, 999999),
        )

        articles = Article.objects.filter(
            pub_date__year=2008).extra(select={'dashed-value': '1', 'undashedvalue': '2'})
        self.assertEqual(articles[0].undashedvalue, 2)

    def test_create_relation_with_ugettext_lazy(self):
        """
        Test that ugettext_lazy objects work when saving model instances
        through various methods. Refs #10498.
        """
        notlazy = 'test'
        lazy = ugettext_lazy(notlazy)
        Article.objects.create(headline=lazy, pub_date=datetime.now())
        article = Article.objects.get()
        self.assertEqual(article.headline, notlazy)
        # test that assign + save works with Promise objects
        article.headline = lazy
        article.save()
        self.assertEqual(article.headline, notlazy)
        # test .update()
        Article.objects.update(headline=lazy)
        article = Article.objects.get()
        self.assertEqual(article.headline, notlazy)
        # still test bulk_create()
        Article.objects.all().delete()
        Article.objects.bulk_create([Article(headline=lazy, pub_date=datetime.now())])
        article = Article.objects.get()
        self.assertEqual(article.headline, notlazy)

    def test_emptyqs(self):
        # Can't be instantiated
        with self.assertRaises(TypeError):
            EmptyQuerySet()
        self.assertIsInstance(Article.objects.none(), EmptyQuerySet)

    def test_emptyqs_values(self):
        # test for #15959
        Article.objects.create(headline='foo', pub_date=datetime.now())
        with self.assertNumQueries(0):
            qs = Article.objects.none().values_list('pk')
            self.assertIsInstance(qs, EmptyQuerySet)
            self.assertEqual(len(qs), 0)

    def test_emptyqs_customqs(self):
        # A hacky test for custom QuerySet subclass - refs #17271
        Article.objects.create(headline='foo', pub_date=datetime.now())

        class CustomQuerySet(QuerySet):
            def do_something(self):
                return 'did something'

        qs = Article.objects.all()
        qs.__class__ = CustomQuerySet
        qs = qs.none()
        with self.assertNumQueries(0):
            self.assertEqual(len(qs), 0)
            self.assertIsInstance(qs, EmptyQuerySet)
            self.assertEqual(qs.do_something(), 'did something')

    def test_emptyqs_values_order(self):
        # Tests for ticket #17712
        Article.objects.create(headline='foo', pub_date=datetime.now())
        with self.assertNumQueries(0):
            self.assertEqual(len(Article.objects.none().values_list('id').order_by('id')), 0)
        with self.assertNumQueries(0):
            self.assertEqual(len(Article.objects.none().filter(
                id__in=Article.objects.values_list('id', flat=True))), 0)

    @skipUnlessDBFeature('can_distinct_on_fields')
    def test_emptyqs_distinct(self):
        # Tests for #19426
        Article.objects.create(headline='foo', pub_date=datetime.now())
        with self.assertNumQueries(0):
            self.assertEqual(len(Article.objects.none().distinct('headline', 'pub_date')), 0)

    def test_ticket_20278(self):
        sr = SelfRef.objects.create()
        with self.assertRaises(ObjectDoesNotExist):
            SelfRef.objects.get(selfref=sr)

    def test_eq(self):
        self.assertEqual(Article(id=1), Article(id=1))
        self.assertNotEqual(Article(id=1), object())
        self.assertNotEqual(object(), Article(id=1))
        a = Article()
        self.assertEqual(a, a)
        self.assertNotEqual(Article(), a)

    def test_hash(self):
        # Value based on PK
        self.assertEqual(hash(Article(id=1)), hash(1))
        with self.assertRaises(TypeError):
            # No PK value -> unhashable (because save() would then change
            # hash)
            hash(Article())


class ModelLookupTest(TestCase):
    def setUp(self):
        # Create an Article.
        self.a = Article(
            id=None,
            headline='Area woman programs in Python',
            pub_date=datetime(2005, 7, 28),
        )
        # Save it into the database. You have to call save() explicitly.
        self.a.save()

    def test_all_lookup(self):
        # Change values by changing the attributes, then calling save().
        self.a.headline = 'Area man programs in Python'
        self.a.save()

        # Article.objects.all() returns all the articles in the database.
        self.assertQuerysetEqual(Article.objects.all(),
            ['<Article: Area man programs in Python>'])

    def test_rich_lookup(self):
        # Django provides a rich database lookup API.
        self.assertEqual(Article.objects.get(id__exact=self.a.id), self.a)
        self.assertEqual(Article.objects.get(headline__startswith='Area woman'), self.a)
        self.assertEqual(Article.objects.get(pub_date__year=2005), self.a)
        self.assertEqual(Article.objects.get(pub_date__year=2005, pub_date__month=7), self.a)
        self.assertEqual(Article.objects.get(pub_date__year=2005, pub_date__month=7, pub_date__day=28), self.a)
        self.assertEqual(Article.objects.get(pub_date__week_day=5), self.a)

    def test_equal_lookup(self):
        # The "__exact" lookup type can be omitted, as a shortcut.
        self.assertEqual(Article.objects.get(id=self.a.id), self.a)
        self.assertEqual(Article.objects.get(headline='Area woman programs in Python'), self.a)

        self.assertQuerysetEqual(
            Article.objects.filter(pub_date__year=2005),
            ['<Article: Area woman programs in Python>'],
        )
        self.assertQuerysetEqual(
            Article.objects.filter(pub_date__year=2004),
            [],
        )
        self.assertQuerysetEqual(
            Article.objects.filter(pub_date__year=2005, pub_date__month=7),
            ['<Article: Area woman programs in Python>'],
        )

        self.assertQuerysetEqual(
            Article.objects.filter(pub_date__week_day=5),
            ['<Article: Area woman programs in Python>'],
        )
        self.assertQuerysetEqual(
            Article.objects.filter(pub_date__week_day=6),
            [],
        )

    def test_does_not_exist(self):
        # Django raises an Article.DoesNotExist exception for get() if the
        # parameters don't match any object.
        six.assertRaisesRegex(
            self,
            ObjectDoesNotExist,
            "Article matching query does not exist.",
            Article.objects.get,
            id__exact=2000,
        )
        # To avoid dict-ordering related errors check only one lookup
        # in single assert.
        self.assertRaises(
            ObjectDoesNotExist,
            Article.objects.get,
            pub_date__year=2005,
            pub_date__month=8,
        )
        six.assertRaisesRegex(
            self,
            ObjectDoesNotExist,
            "Article matching query does not exist.",
            Article.objects.get,
            pub_date__week_day=6,
        )

    def test_lookup_by_primary_key(self):
        # Lookup by a primary key is the most common case, so Django
        # provides a shortcut for primary-key exact lookups.
        # The following is identical to articles.get(id=a.id).
        self.assertEqual(Article.objects.get(pk=self.a.id), self.a)

        # pk can be used as a shortcut for the primary key name in any query.
        self.assertQuerysetEqual(Article.objects.filter(pk__in=[self.a.id]),
            ["<Article: Area woman programs in Python>"])

        # Model instances of the same type and same ID are considered equal.
        a = Article.objects.get(pk=self.a.id)
        b = Article.objects.get(pk=self.a.id)
        self.assertEqual(a, b)

    def test_too_many(self):
        # Create a very similar object
        a = Article(
            id=None,
            headline='Area man programs in Python',
            pub_date=datetime(2005, 7, 28),
        )
        a.save()

        self.assertEqual(Article.objects.count(), 2)

        # Django raises an Article.MultipleObjectsReturned exception if the
        # lookup matches more than one object
        six.assertRaisesRegex(
            self,
            MultipleObjectsReturned,
            "get\(\) returned more than one Article -- it returned 2!",
            Article.objects.get,
            headline__startswith='Area',
        )
        six.assertRaisesRegex(
            self,
            MultipleObjectsReturned,
            "get\(\) returned more than one Article -- it returned 2!",
            Article.objects.get,
            pub_date__year=2005,
        )
        six.assertRaisesRegex(
            self,
            MultipleObjectsReturned,
            "get\(\) returned more than one Article -- it returned 2!",
            Article.objects.get,
            pub_date__year=2005,
            pub_date__month=7,
        )


class ConcurrentSaveTests(TransactionTestCase):

    available_apps = ['basic']

    @skipUnlessDBFeature('test_db_allows_multiple_connections')
    def test_concurrent_delete_with_save(self):
        """
        Test fetching, deleting and finally saving an object - we should get
        an insert in this case.
        """
        a = Article.objects.create(headline='foo', pub_date=datetime.now())
        exceptions = []

        def deleter():
            try:
                # Do not delete a directly - doing so alters its state.
                Article.objects.filter(pk=a.pk).delete()
            except Exception as e:
                exceptions.append(e)
            finally:
                connections[DEFAULT_DB_ALIAS].close()
        self.assertEqual(len(exceptions), 0)
        t = threading.Thread(target=deleter)
        t.start()
        t.join()
        a.save()
        self.assertEqual(Article.objects.get(pk=a.pk).headline, 'foo')


class ManagerTest(TestCase):
    QUERYSET_PROXY_METHODS = [
        'none',
        'count',
        'dates',
        'datetimes',
        'distinct',
        'extra',
        'get',
        'get_or_create',
        'update_or_create',
        'create',
        'bulk_create',
        'filter',
        'aggregate',
        'annotate',
        'complex_filter',
        'exclude',
        'in_bulk',
        'iterator',
        'earliest',
        'latest',
        'first',
        'last',
        'order_by',
        'select_for_update',
        'select_related',
        'prefetch_related',
        'values',
        'values_list',
        'update',
        'reverse',
        'defer',
        'only',
        'using',
        'exists',
        '_insert',
        '_update',
        'raw',
    ]

    def test_manager_methods(self):
        """
        This test ensures that the correct set of methods from `QuerySet`
        are copied onto `Manager`.

        It's particularly useful to prevent accidentally leaking new methods
        into `Manager`. New `QuerySet` methods that should also be copied onto
        `Manager` will need to be added to `ManagerTest.QUERYSET_PROXY_METHODS`.
        """
        self.assertEqual(
            sorted(BaseManager._get_queryset_methods(QuerySet).keys()),
            sorted(self.QUERYSET_PROXY_METHODS),
        )


class SelectOnSaveTests(TestCase):
    def test_select_on_save(self):
        a1 = Article.objects.create(pub_date=datetime.now())
        with self.assertNumQueries(1):
            a1.save()
        asos = ArticleSelectOnSave.objects.create(pub_date=datetime.now())
        with self.assertNumQueries(2):
            asos.save()
        with self.assertNumQueries(1):
            asos.save(force_update=True)
        Article.objects.all().delete()
        with self.assertRaises(DatabaseError):
            with self.assertNumQueries(1):
                asos.save(force_update=True)

    def test_select_on_save_lying_update(self):
        """
        Test that select_on_save works correctly if the database
        doesn't return correct information about matched rows from
        UPDATE.
        """
        # Change the manager to not return "row matched" for update().
        # We are going to change the Article's _base_manager class
        # dynamically. This is a bit of a hack, but it seems hard to
        # test this properly otherwise. Article's manager, because
        # proxy models use their parent model's _base_manager.

        orig_class = Article._base_manager.__class__

        class FakeQuerySet(QuerySet):
            # Make sure the _update method below is in fact called.
            called = False

            def _update(self, *args, **kwargs):
                FakeQuerySet.called = True
                super(FakeQuerySet, self)._update(*args, **kwargs)
                return 0

        class FakeManager(orig_class):
            def get_queryset(self):
                return FakeQuerySet(self.model)
        try:
            Article._base_manager.__class__ = FakeManager
            asos = ArticleSelectOnSave.objects.create(pub_date=datetime.now())
            with self.assertNumQueries(3):
                asos.save()
                self.assertTrue(FakeQuerySet.called)
            # This is not wanted behavior, but this is how Django has always
            # behaved for databases that do not return correct information
            # about matched rows for UPDATE.
            with self.assertRaises(DatabaseError):
                asos.save(force_update=True)
            with self.assertRaises(DatabaseError):
                asos.save(update_fields=['pub_date'])
        finally:
            Article._base_manager.__class__ = orig_class


class ModelRefreshTests(TestCase):
    def _truncate_ms(self, val):
        # MySQL < 5.6.4 removes microseconds from the datetimes which can cause
        # problems when comparing the original value to that loaded from DB
        return val - timedelta(microseconds=val.microsecond)

    def test_refresh(self):
        a = Article.objects.create(pub_date=self._truncate_ms(datetime.now()))
        Article.objects.create(pub_date=self._truncate_ms(datetime.now()))
        Article.objects.filter(pk=a.pk).update(headline='new headline')
        with self.assertNumQueries(1):
            a.refresh_from_db()
            self.assertEqual(a.headline, 'new headline')

        orig_pub_date = a.pub_date
        new_pub_date = a.pub_date + timedelta(10)
        Article.objects.update(headline='new headline 2', pub_date=new_pub_date)
        with self.assertNumQueries(1):
            a.refresh_from_db(fields=['headline'])
            self.assertEqual(a.headline, 'new headline 2')
            self.assertEqual(a.pub_date, orig_pub_date)
        with self.assertNumQueries(1):
            a.refresh_from_db()
            self.assertEqual(a.pub_date, new_pub_date)

    def test_refresh_fk(self):
        s1 = SelfRef.objects.create()
        s2 = SelfRef.objects.create()
        s3 = SelfRef.objects.create(selfref=s1)
        s3_copy = SelfRef.objects.get(pk=s3.pk)
        s3_copy.selfref.touched = True
        s3.selfref = s2
        s3.save()
        with self.assertNumQueries(1):
            s3_copy.refresh_from_db()
        with self.assertNumQueries(1):
            # The old related instance was thrown away (the selfref_id has
            # changed). It needs to be reloaded on access, so one query
            # executed.
            self.assertFalse(hasattr(s3_copy.selfref, 'touched'))
            self.assertEqual(s3_copy.selfref, s2)

    def test_refresh_unsaved(self):
        pub_date = self._truncate_ms(datetime.now())
        a = Article.objects.create(pub_date=pub_date)
        a2 = Article(id=a.pk)
        with self.assertNumQueries(1):
            a2.refresh_from_db()
        self.assertEqual(a2.pub_date, pub_date)
        self.assertEqual(a2._state.db, "default")

    def test_refresh_no_fields(self):
        a = Article.objects.create(pub_date=self._truncate_ms(datetime.now()))
        with self.assertNumQueries(0):
            a.refresh_from_db(fields=[])


class TestRelatedObjectDeprecation(TestCase):
    def test_field_related_deprecation(self):
        field = SelfRef._meta.get_field('selfref')
        with warnings.catch_warnings(record=True) as warns:
            warnings.simplefilter('always')
            self.assertIsInstance(field.related, ForeignObjectRel)
            self.assertEqual(len(warns), 1)
            self.assertEqual(
                str(warns.pop().message),
                'Usage of field.related has been deprecated. Use field.rel instead.'
            )