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# Copyright 2011 Canonical Ltd. This software is licensed under the
# GNU Affero General Public License version 3 (see the file LICENSE).
"""Test `TransactionPolicy`."""
__metaclass__ = type
from psycopg2 import InternalError
import transaction
from lp.registry.model.person import Person
from lp.services.database.isolation import (
check_no_transaction,
TransactionInProgress,
)
from lp.services.database.lpstorm import IStore
from lp.services.database.transaction_policy import DatabaseTransactionPolicy
from lp.testing import TestCaseWithFactory
from lp.testing.layers import ZopelessDatabaseLayer
class TestTransactionPolicy(TestCaseWithFactory):
layer = ZopelessDatabaseLayer
def setUp(self):
super(TestTransactionPolicy, self).setUp()
# Start each test with a clean slate: no ongoing transaction
# unless the test says so.
transaction.abort()
def readFromDatabase(self):
"""Perform a database read."""
IStore(Person).find(Person, Person.name == "arbitrary").first()
def writeToDatabase(self):
"""Write an object to the database.
:return: A token that `hasDatabaseBeenWrittenTo` can look for.
"""
name = self.factory.getUniqueString()
self.factory.makePerson(name=name)
return name
def writeToDatabaseAndCommit(self):
"""Write an object to the database and commit.
:return: A token that `hasDatabaseBeenWrittenTo` can look for.
"""
name = self.writeToDatabase()
transaction.commit()
return name
def hasDatabaseBeenWrittenTo(self, test_token):
"""Is the object made by `writeToDatabase` present in the database?
:param test_token: The return value from `writeToDatabase`.
:return: Has the change represented by `test_token` been made to the
database?
"""
query = IStore(Person).find(Person, Person.name == test_token)
return query.one() is not None
def test_can_be_empty(self):
# An empty transaction policy works fine.
with DatabaseTransactionPolicy():
pass
# You still end up with a clean slate, transaction-wise.
check_no_transaction()
def test_writable_permits_updates(self):
# Writes to the database work just fine in a non-read-only
# policy.
with DatabaseTransactionPolicy(read_only=False):
self.writeToDatabase()
transaction.commit()
# The test is that we get here without failure.
pass
def test_readonly_forbids_updates(self):
# A read-only policy forbids writes to the database.
def make_forbidden_update():
with DatabaseTransactionPolicy(read_only=True):
self.writeToDatabase()
transaction.commit()
self.assertRaises(InternalError, make_forbidden_update)
def test_will_not_go_read_only_when_read_write_transaction_ongoing(self):
# You cannot enter a read-only DatabaseTransactionPolicy while in an
# active read-write transaction.
def enter_policy():
with DatabaseTransactionPolicy(read_only=True):
pass
self.writeToDatabase()
self.assertRaises(TransactionInProgress, enter_policy)
def test_will_go_read_write_when_read_write_transaction_ongoing(self):
# You can enter a read-write DatabaseTransactionPolicy while in an
# active read-write transaction.
def enter_policy():
with DatabaseTransactionPolicy(read_only=False):
pass
self.writeToDatabase()
enter_policy() # No exception.
def test_successful_exit_requires_commit_or_abort(self):
# If a read-write policy exits normally (which would probably
# indicate successful completion of its code), it requires that
# any ongoing transaction be committed or aborted first.
test_token = None
def leave_transaction_open():
with DatabaseTransactionPolicy(read_only=False):
self.writeToDatabase()
self.assertRaises(TransactionInProgress, leave_transaction_open)
# As a side effect of the error, the transaction is rolled back.
self.assertFalse(self.hasDatabaseBeenWrittenTo(test_token))
def test_successful_read_only_exit_commits_or_aborts_implicitly(self):
# When a read-only policy exits normally, there is no need to
# complete the transaction. It aborts or commits implicitly.
# (The choice is up to the implementation; the point of
# read-only is that you can't tell the difference.)
with DatabaseTransactionPolicy(read_only=True):
self.readFromDatabase()
# No transaction ongoing at this point.
check_no_transaction()
def test_aborts_on_failure(self):
# If the context handler exits with an exception, it aborts the
# transaction.
class CompleteFailure(Exception):
pass
try:
with DatabaseTransactionPolicy(read_only=False):
test_token = self.writeToDatabase()
raise CompleteFailure()
except CompleteFailure:
pass
# No transaction ongoing at this point.
check_no_transaction()
# The change has rolled back.
self.assertFalse(self.hasDatabaseBeenWrittenTo(test_token))
def test_nested_policy_overrides_previous_policy(self):
# When one policy is nested in another, the nested one
# determines what is allowed.
def allows_updates(read_only=True):
"""Does the given policy permit database updates?"""
try:
with DatabaseTransactionPolicy(read_only=read_only):
self.writeToDatabase()
transaction.commit()
return True
except InternalError:
return False
# Map (previous policy, nested policy) to whether the
# combination makes the store read-only.
effects = {}
for previous_policy in [False, True]:
for nested_policy in [False, True]:
experiment = (previous_policy, nested_policy)
with DatabaseTransactionPolicy(read_only=previous_policy):
is_read_only = not allows_updates(nested_policy)
effects[experiment] = is_read_only
# Only the nested policy (the second element of the key tuple)
# determines whether writes are allowed (the value associated
# with the key).
self.assertEqual({
(False, False): False,
(False, True): True,
(True, False): False,
(True, True): True,
},
effects)
def test_policy_restores_previous_policy_on_success(self):
# A transaction policy, once exited, restores the previously
# applicable policy.
with DatabaseTransactionPolicy(read_only=False):
with DatabaseTransactionPolicy(read_only=True):
self.readFromDatabase()
self.assertTrue(
self.hasDatabaseBeenWrittenTo(self.writeToDatabase()))
transaction.commit()
self.assertTrue(
self.hasDatabaseBeenWrittenTo(self.writeToDatabase()))
def test_propagates_failure(self):
# Exceptions raised inside a transaction policy are not
# swallowed.
class Kaboom(Exception):
pass
def fail_within_policy():
with DatabaseTransactionPolicy():
raise Kaboom()
self.assertRaises(Kaboom, fail_within_policy)
def test_policy_restores_previous_policy_on_failure(self):
# A transaction policy restores the previously applicable policy
# even when it exits abnormally.
class HorribleFailure(Exception):
pass
try:
with DatabaseTransactionPolicy(read_only=True):
raise HorribleFailure()
except HorribleFailure:
pass
self.assertTrue(
self.hasDatabaseBeenWrittenTo(self.writeToDatabase()))
def test_policy_can_span_transactions(self):
# It's okay to commit within a policy; the policy will still
# apply to the next transaction inside the same policy.
test_token = self.writeToDatabase()
transaction.commit()
with DatabaseTransactionPolicy(read_only=True):
self.hasDatabaseBeenWrittenTo(test_token)
transaction.commit()
self.assertRaises(InternalError, self.writeToDatabaseAndCommit)
transaction.abort()
def test_policy_survives_abort(self):
# Even after aborting the initial transaction, a transaction
# policy still applies.
with DatabaseTransactionPolicy(read_only=True):
self.readFromDatabase()
transaction.abort()
self.assertRaises(InternalError, self.writeToDatabaseAndCommit)
transaction.abort()
def test_readOnly(self):
# DatabaseTransactionPolicy.readOnly() is a function decorator that
# applies a read-only policy for the duration of the function call.
writeToDatabaseAndCommit = DatabaseTransactionPolicy.readOnly(
self.writeToDatabaseAndCommit)
with DatabaseTransactionPolicy(read_only=False):
self.assertRaises(InternalError, writeToDatabaseAndCommit)
def test_readWrite(self):
# DatabaseTransactionPolicy.readWrite() is a function decorator that
# applies a read-write policy for the duration of the function call.
writeToDatabaseAndCommit = DatabaseTransactionPolicy.readWrite(
self.writeToDatabaseAndCommit)
with DatabaseTransactionPolicy(read_only=True):
writeToDatabaseAndCommit() # No exception.
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