django/tests/select_for_update/tests.py

import threading
import time
from unittest import mock

from multiple_database.routers import TestRouter

from django.core.exceptions import FieldError
from django.db import (
    DatabaseError,
    NotSupportedError,
    connection,
    connections,
    router,
    transaction,
)
from django.test import (
    TransactionTestCase,
    override_settings,
    skipIfDBFeature,
    skipUnlessDBFeature,
)
from django.test.utils import CaptureQueriesContext

from .models import (
    City,
    CityCountryProxy,
    Country,
    EUCity,
    EUCountry,
    Person,
    PersonProfile,
)


class SelectForUpdateTests(TransactionTestCase):

    available_apps = ["select_for_update"]

    def setUp(self):
        # This is executed in autocommit mode so that code in
        # run_select_for_update can see this data.
        self.country1 = Country.objects.create(name="Belgium")
        self.country2 = Country.objects.create(name="France")
        self.city1 = City.objects.create(name="Liberchies", country=self.country1)
        self.city2 = City.objects.create(name="Samois-sur-Seine", country=self.country2)
        self.person = Person.objects.create(
            name="Reinhardt", born=self.city1, died=self.city2
        )
        self.person_profile = PersonProfile.objects.create(person=self.person)

        # We need another database connection in transaction to test that one
        # connection issuing a SELECT ... FOR UPDATE will block.
        self.new_connection = connection.copy()

    def tearDown(self):
        try:
            self.end_blocking_transaction()
        except (DatabaseError, AttributeError):
            pass
        self.new_connection.close()

    def start_blocking_transaction(self):
        self.new_connection.set_autocommit(False)
        # Start a blocking transaction. At some point,
        # end_blocking_transaction() should be called.
        self.cursor = self.new_connection.cursor()
        sql = "SELECT * FROM %(db_table)s %(for_update)s;" % {
            "db_table": Person._meta.db_table,
            "for_update": self.new_connection.ops.for_update_sql(),
        }
        self.cursor.execute(sql, ())
        self.cursor.fetchone()

    def end_blocking_transaction(self):
        # Roll back the blocking transaction.
        self.cursor.close()
        self.new_connection.rollback()
        self.new_connection.set_autocommit(True)

    def has_for_update_sql(self, queries, **kwargs):
        # Examine the SQL that was executed to determine whether it
        # contains the 'SELECT..FOR UPDATE' stanza.
        for_update_sql = connection.ops.for_update_sql(**kwargs)
        return any(for_update_sql in query["sql"] for query in queries)

    @skipUnlessDBFeature("has_select_for_update")
    def test_for_update_sql_generated(self):
        """
        The backend's FOR UPDATE variant appears in
        generated SQL when select_for_update is invoked.
        """
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(Person.objects.all().select_for_update())
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries))

    @skipUnlessDBFeature("has_select_for_update_nowait")
    def test_for_update_sql_generated_nowait(self):
        """
        The backend's FOR UPDATE NOWAIT variant appears in
        generated SQL when select_for_update is invoked.
        """
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(Person.objects.all().select_for_update(nowait=True))
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, nowait=True))

    @skipUnlessDBFeature("has_select_for_update_skip_locked")
    def test_for_update_sql_generated_skip_locked(self):
        """
        The backend's FOR UPDATE SKIP LOCKED variant appears in
        generated SQL when select_for_update is invoked.
        """
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(Person.objects.all().select_for_update(skip_locked=True))
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, skip_locked=True))

    @skipUnlessDBFeature("has_select_for_no_key_update")
    def test_update_sql_generated_no_key(self):
        """
        The backend's FOR NO KEY UPDATE variant appears in generated SQL when
        select_for_update() is invoked.
        """
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(Person.objects.all().select_for_update(no_key=True))
        self.assertIs(self.has_for_update_sql(ctx.captured_queries, no_key=True), True)

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_generated_of(self):
        """
        The backend's FOR UPDATE OF variant appears in the generated SQL when
        select_for_update() is invoked.
        """
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                Person.objects.select_related(
                    "born__country",
                )
                .select_for_update(
                    of=("born__country",),
                )
                .select_for_update(of=("self", "born__country"))
            )
        features = connections["default"].features
        if features.select_for_update_of_column:
            expected = [
                'select_for_update_person"."id',
                'select_for_update_country"."entity_ptr_id',
            ]
        else:
            expected = ["select_for_update_person", "select_for_update_country"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_model_inheritance_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(EUCountry.objects.select_for_update(of=("self",)))
        if connection.features.select_for_update_of_column:
            expected = ['select_for_update_eucountry"."country_ptr_id']
        else:
            expected = ["select_for_update_eucountry"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_model_inheritance_ptr_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                EUCountry.objects.select_for_update(
                    of=(
                        "self",
                        "country_ptr",
                    )
                )
            )
        if connection.features.select_for_update_of_column:
            expected = [
                'select_for_update_eucountry"."country_ptr_id',
                'select_for_update_country"."entity_ptr_id',
            ]
        else:
            expected = ["select_for_update_eucountry", "select_for_update_country"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_related_model_inheritance_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                EUCity.objects.select_related("country").select_for_update(
                    of=("self", "country"),
                )
            )
        if connection.features.select_for_update_of_column:
            expected = [
                'select_for_update_eucity"."id',
                'select_for_update_eucountry"."country_ptr_id',
            ]
        else:
            expected = ["select_for_update_eucity", "select_for_update_eucountry"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_model_inheritance_nested_ptr_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                EUCity.objects.select_related("country").select_for_update(
                    of=(
                        "self",
                        "country__country_ptr",
                    ),
                )
            )
        if connection.features.select_for_update_of_column:
            expected = [
                'select_for_update_eucity"."id',
                'select_for_update_country"."entity_ptr_id',
            ]
        else:
            expected = ["select_for_update_eucity", "select_for_update_country"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_multilevel_model_inheritance_ptr_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                EUCountry.objects.select_for_update(
                    of=("country_ptr", "country_ptr__entity_ptr"),
                )
            )
        if connection.features.select_for_update_of_column:
            expected = [
                'select_for_update_country"."entity_ptr_id',
                'select_for_update_entity"."id',
            ]
        else:
            expected = ["select_for_update_country", "select_for_update_entity"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_sql_model_proxy_generated_of(self):
        with transaction.atomic(), CaptureQueriesContext(connection) as ctx:
            list(
                CityCountryProxy.objects.select_related("country",).select_for_update(
                    of=("country",),
                )
            )
        if connection.features.select_for_update_of_column:
            expected = ['select_for_update_country"."entity_ptr_id']
        else:
            expected = ["select_for_update_country"]
        expected = [connection.ops.quote_name(value) for value in expected]
        self.assertTrue(self.has_for_update_sql(ctx.captured_queries, of=expected))

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_of_followed_by_values(self):
        with transaction.atomic():
            values = list(Person.objects.select_for_update(of=("self",)).values("pk"))
        self.assertEqual(values, [{"pk": self.person.pk}])

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_of_followed_by_values_list(self):
        with transaction.atomic():
            values = list(
                Person.objects.select_for_update(of=("self",)).values_list("pk")
            )
        self.assertEqual(values, [(self.person.pk,)])

    @skipUnlessDBFeature("has_select_for_update_of")
    def test_for_update_of_self_when_self_is_not_selected(self):
        """
        select_for_update(of=['self']) when the only columns selected are from
        related tables.
        """
        with transaction.atomic():
            values = list(
                Person.objects.select_related("born")
                .select_for_update(of=("self",))
                .values("born__name")
            )
        self.assertEqual(values, [{"born__name": self.city1.name}])

    @skipUnlessDBFeature(
        "has_select_for_update_of",
        "supports_select_for_update_with_limit",
    )
    def test_for_update_of_with_exists(self):
        with transaction.atomic():
            qs = Person.objects.select_for_update(of=("self", "born"))
            self.assertIs(qs.exists(), True)

    @skipUnlessDBFeature("has_select_for_update_nowait")
    def test_nowait_raises_error_on_block(self):
        """
        If nowait is specified, we expect an error to be raised rather
        than blocking.
        """
        self.start_blocking_transaction()
        status = []

        thread = threading.Thread(
            target=self.run_select_for_update,
            args=(status,),
            kwargs={"nowait": True},
        )

        thread.start()
        time.sleep(1)
        thread.join()
        self.end_blocking_transaction()
        self.assertIsInstance(status[-1], DatabaseError)

    @skipUnlessDBFeature("has_select_for_update_skip_locked")
    def test_skip_locked_skips_locked_rows(self):
        """
        If skip_locked is specified, the locked row is skipped resulting in
        Person.DoesNotExist.
        """
        self.start_blocking_transaction()
        status = []
        thread = threading.Thread(
            target=self.run_select_for_update,
            args=(status,),
            kwargs={"skip_locked": True},
        )
        thread.start()
        time.sleep(1)
        thread.join()
        self.end_blocking_transaction()
        self.assertIsInstance(status[-1], Person.DoesNotExist)

    @skipIfDBFeature("has_select_for_update_nowait")
    @skipUnlessDBFeature("has_select_for_update")
    def test_unsupported_nowait_raises_error(self):
        """
        NotSupportedError is raised if a SELECT...FOR UPDATE NOWAIT is run on
        a database backend that supports FOR UPDATE but not NOWAIT.
        """
        with self.assertRaisesMessage(
            NotSupportedError, "NOWAIT is not supported on this database backend."
        ):
            with transaction.atomic():
                Person.objects.select_for_update(nowait=True).get()

    @skipIfDBFeature("has_select_for_update_skip_locked")
    @skipUnlessDBFeature("has_select_for_update")
    def test_unsupported_skip_locked_raises_error(self):
        """
        NotSupportedError is raised if a SELECT...FOR UPDATE SKIP LOCKED is run
        on a database backend that supports FOR UPDATE but not SKIP LOCKED.
        """
        with self.assertRaisesMessage(
            NotSupportedError, "SKIP LOCKED is not supported on this database backend."
        ):
            with transaction.atomic():
                Person.objects.select_for_update(skip_locked=True).get()

    @skipIfDBFeature("has_select_for_update_of")
    @skipUnlessDBFeature("has_select_for_update")
    def test_unsupported_of_raises_error(self):
        """
        NotSupportedError is raised if a SELECT...FOR UPDATE OF... is run on
        a database backend that supports FOR UPDATE but not OF.
        """
        msg = "FOR UPDATE OF is not supported on this database backend."
        with self.assertRaisesMessage(NotSupportedError, msg):
            with transaction.atomic():
                Person.objects.select_for_update(of=("self",)).get()

    @skipIfDBFeature("has_select_for_no_key_update")
    @skipUnlessDBFeature("has_select_for_update")
    def test_unsuported_no_key_raises_error(self):
        """
        NotSupportedError is raised if a SELECT...FOR NO KEY UPDATE... is run
        on a database backend that supports FOR UPDATE but not NO KEY.
        """
        msg = "FOR NO KEY UPDATE is not supported on this database backend."
        with self.assertRaisesMessage(NotSupportedError, msg):
            with transaction.atomic():
                Person.objects.select_for_update(no_key=True).get()

    @skipUnlessDBFeature("has_select_for_update", "has_select_for_update_of")
    def test_unrelated_of_argument_raises_error(self):
        """
        FieldError is raised if a non-relation field is specified in of=(...).
        """
        msg = (
            "Invalid field name(s) given in select_for_update(of=(...)): %s. "
            "Only relational fields followed in the query are allowed. "
            "Choices are: self, born, born__country, "
            "born__country__entity_ptr."
        )
        invalid_of = [
            ("nonexistent",),
            ("name",),
            ("born__nonexistent",),
            ("born__name",),
            ("born__nonexistent", "born__name"),
        ]
        for of in invalid_of:
            with self.subTest(of=of):
                with self.assertRaisesMessage(FieldError, msg % ", ".join(of)):
                    with transaction.atomic():
                        Person.objects.select_related(
                            "born__country"
                        ).select_for_update(of=of).get()

    @skipUnlessDBFeature("has_select_for_update", "has_select_for_update_of")
    def test_related_but_unselected_of_argument_raises_error(self):
        """
        FieldError is raised if a relation field that is not followed in the
        query is specified in of=(...).
        """
        msg = (
            "Invalid field name(s) given in select_for_update(of=(...)): %s. "
            "Only relational fields followed in the query are allowed. "
            "Choices are: self, born, profile."
        )
        for name in ["born__country", "died", "died__country"]:
            with self.subTest(name=name):
                with self.assertRaisesMessage(FieldError, msg % name):
                    with transaction.atomic():
                        Person.objects.select_related("born", "profile",).exclude(
                            profile=None
                        ).select_for_update(of=(name,)).get()

    @skipUnlessDBFeature("has_select_for_update", "has_select_for_update_of")
    def test_model_inheritance_of_argument_raises_error_ptr_in_choices(self):
        msg = (
            "Invalid field name(s) given in select_for_update(of=(...)): "
            "name. Only relational fields followed in the query are allowed. "
            "Choices are: self, %s."
        )
        with self.assertRaisesMessage(
            FieldError,
            msg % "country, country__country_ptr, country__country_ptr__entity_ptr",
        ):
            with transaction.atomic():
                EUCity.objects.select_related(
                    "country",
                ).select_for_update(of=("name",)).get()
        with self.assertRaisesMessage(
            FieldError, msg % "country_ptr, country_ptr__entity_ptr"
        ):
            with transaction.atomic():
                EUCountry.objects.select_for_update(of=("name",)).get()

    @skipUnlessDBFeature("has_select_for_update", "has_select_for_update_of")
    def test_model_proxy_of_argument_raises_error_proxy_field_in_choices(self):
        msg = (
            "Invalid field name(s) given in select_for_update(of=(...)): "
            "name. Only relational fields followed in the query are allowed. "
            "Choices are: self, country, country__entity_ptr."
        )
        with self.assertRaisesMessage(FieldError, msg):
            with transaction.atomic():
                CityCountryProxy.objects.select_related(
                    "country",
                ).select_for_update(of=("name",)).get()

    @skipUnlessDBFeature("has_select_for_update", "has_select_for_update_of")
    def test_reverse_one_to_one_of_arguments(self):
        """
        Reverse OneToOneFields may be included in of=(...) as long as NULLs
        are excluded because LEFT JOIN isn't allowed in SELECT FOR UPDATE.
        """
        with transaction.atomic():
            person = (
                Person.objects.select_related(
                    "profile",
                )
                .exclude(profile=None)
                .select_for_update(of=("profile",))
                .get()
            )
            self.assertEqual(person.profile, self.person_profile)

    @skipUnlessDBFeature("has_select_for_update")
    def test_for_update_after_from(self):
        features_class = connections["default"].features.__class__
        attribute_to_patch = "%s.%s.for_update_after_from" % (
            features_class.__module__,
            features_class.__name__,
        )
        with mock.patch(attribute_to_patch, return_value=True):
            with transaction.atomic():
                self.assertIn(
                    "FOR UPDATE WHERE",
                    str(Person.objects.filter(name="foo").select_for_update().query),
                )

    @skipUnlessDBFeature("has_select_for_update")
    def test_for_update_requires_transaction(self):
        """
        A TransactionManagementError is raised
        when a select_for_update query is executed outside of a transaction.
        """
        msg = "select_for_update cannot be used outside of a transaction."
        with self.assertRaisesMessage(transaction.TransactionManagementError, msg):
            list(Person.objects.all().select_for_update())

    @skipUnlessDBFeature("has_select_for_update")
    def test_for_update_requires_transaction_only_in_execution(self):
        """
        No TransactionManagementError is raised
        when select_for_update is invoked outside of a transaction -
        only when the query is executed.
        """
        people = Person.objects.all().select_for_update()
        msg = "select_for_update cannot be used outside of a transaction."
        with self.assertRaisesMessage(transaction.TransactionManagementError, msg):
            list(people)

    @skipUnlessDBFeature("supports_select_for_update_with_limit")
    def test_select_for_update_with_limit(self):
        other = Person.objects.create(name="Grappeli", born=self.city1, died=self.city2)
        with transaction.atomic():
            qs = list(Person.objects.all().order_by("pk").select_for_update()[1:2])
            self.assertEqual(qs[0], other)

    @skipIfDBFeature("supports_select_for_update_with_limit")
    def test_unsupported_select_for_update_with_limit(self):
        msg = (
            "LIMIT/OFFSET is not supported with select_for_update on this database "
            "backend."
        )
        with self.assertRaisesMessage(NotSupportedError, msg):
            with transaction.atomic():
                list(Person.objects.all().order_by("pk").select_for_update()[1:2])

    def run_select_for_update(self, status, **kwargs):
        """
        Utility method that runs a SELECT FOR UPDATE against all
        Person instances. After the select_for_update, it attempts
        to update the name of the only record, save, and commit.

        This function expects to run in a separate thread.
        """
        status.append("started")
        try:
            # We need to enter transaction management again, as this is done on
            # per-thread basis
            with transaction.atomic():
                person = Person.objects.select_for_update(**kwargs).get()
                person.name = "Fred"
                person.save()
        except (DatabaseError, Person.DoesNotExist) as e:
            status.append(e)
        finally:
            # This method is run in a separate thread. It uses its own
            # database connection. Close it without waiting for the GC.
            connection.close()

    @skipUnlessDBFeature("has_select_for_update")
    @skipUnlessDBFeature("supports_transactions")
    def test_block(self):
        """
        A thread running a select_for_update that accesses rows being touched
        by a similar operation on another connection blocks correctly.
        """
        # First, let's start the transaction in our thread.
        self.start_blocking_transaction()

        # Now, try it again using the ORM's select_for_update
        # facility. Do this in a separate thread.
        status = []
        thread = threading.Thread(target=self.run_select_for_update, args=(status,))

        # The thread should immediately block, but we'll sleep
        # for a bit to make sure.
        thread.start()
        sanity_count = 0
        while len(status) != 1 and sanity_count < 10:
            sanity_count += 1
            time.sleep(1)
        if sanity_count >= 10:
            raise ValueError("Thread did not run and block")

        # Check the person hasn't been updated. Since this isn't
        # using FOR UPDATE, it won't block.
        p = Person.objects.get(pk=self.person.pk)
        self.assertEqual("Reinhardt", p.name)

        # When we end our blocking transaction, our thread should
        # be able to continue.
        self.end_blocking_transaction()
        thread.join(5.0)

        # Check the thread has finished. Assuming it has, we should
        # find that it has updated the person's name.
        self.assertFalse(thread.is_alive())

        # We must commit the transaction to ensure that MySQL gets a fresh read,
        # since by default it runs in REPEATABLE READ mode
        transaction.commit()

        p = Person.objects.get(pk=self.person.pk)
        self.assertEqual("Fred", p.name)

    @skipUnlessDBFeature("has_select_for_update")
    def test_raw_lock_not_available(self):
        """
        Running a raw query which can't obtain a FOR UPDATE lock raises
        the correct exception
        """
        self.start_blocking_transaction()

        def raw(status):
            try:
                list(
                    Person.objects.raw(
                        "SELECT * FROM %s %s"
                        % (
                            Person._meta.db_table,
                            connection.ops.for_update_sql(nowait=True),
                        )
                    )
                )
            except DatabaseError as e:
                status.append(e)
            finally:
                # This method is run in a separate thread. It uses its own
                # database connection. Close it without waiting for the GC.
                # Connection cannot be closed on Oracle because cursor is still
                # open.
                if connection.vendor != "oracle":
                    connection.close()

        status = []
        thread = threading.Thread(target=raw, kwargs={"status": status})
        thread.start()
        time.sleep(1)
        thread.join()
        self.end_blocking_transaction()
        self.assertIsInstance(status[-1], DatabaseError)

    @skipUnlessDBFeature("has_select_for_update")
    @override_settings(DATABASE_ROUTERS=[TestRouter()])
    def test_select_for_update_on_multidb(self):
        query = Person.objects.select_for_update()
        self.assertEqual(router.db_for_write(Person), query.db)

    @skipUnlessDBFeature("has_select_for_update")
    def test_select_for_update_with_get(self):
        with transaction.atomic():
            person = Person.objects.select_for_update().get(name="Reinhardt")
        self.assertEqual(person.name, "Reinhardt")

    def test_nowait_and_skip_locked(self):
        with self.assertRaisesMessage(
            ValueError, "The nowait option cannot be used with skip_locked."
        ):
            Person.objects.select_for_update(nowait=True, skip_locked=True)

    def test_ordered_select_for_update(self):
        """
        Subqueries should respect ordering as an ORDER BY clause may be useful
        to specify a row locking order to prevent deadlocks (#27193).
        """
        with transaction.atomic():
            qs = Person.objects.filter(
                id__in=Person.objects.order_by("-id").select_for_update()
            )
            self.assertIn("ORDER BY", str(qs.query))