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.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.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.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.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", "supports_transactions")
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", "supports_transactions")
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", "supports_transactions")
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.select_for_update())
@skipUnlessDBFeature("has_select_for_update", "supports_transactions")
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.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.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.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", "supports_transactions")
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))