315 lines
12 KiB
Python
315 lines
12 KiB
Python
from functools import wraps
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from django.db import (
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connections, DEFAULT_DB_ALIAS,
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DatabaseError, Error, ProgrammingError)
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from django.utils.decorators import available_attrs
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class TransactionManagementError(ProgrammingError):
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"""
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This exception is thrown when transaction management is used improperly.
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"""
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pass
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def get_connection(using=None):
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"""
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Get a database connection by name, or the default database connection
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if no name is provided. This is a private API.
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"""
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if using is None:
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using = DEFAULT_DB_ALIAS
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return connections[using]
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def get_autocommit(using=None):
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"""
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Get the autocommit status of the connection.
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"""
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return get_connection(using).get_autocommit()
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def set_autocommit(autocommit, using=None):
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"""
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Set the autocommit status of the connection.
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"""
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return get_connection(using).set_autocommit(autocommit)
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def commit(using=None):
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"""
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Commits a transaction.
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"""
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get_connection(using).commit()
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def rollback(using=None):
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"""
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Rolls back a transaction.
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"""
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get_connection(using).rollback()
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def savepoint(using=None):
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"""
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Creates a savepoint (if supported and required by the backend) inside the
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current transaction. Returns an identifier for the savepoint that will be
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used for the subsequent rollback or commit.
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"""
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return get_connection(using).savepoint()
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def savepoint_rollback(sid, using=None):
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"""
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Rolls back the most recent savepoint (if one exists). Does nothing if
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savepoints are not supported.
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"""
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get_connection(using).savepoint_rollback(sid)
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def savepoint_commit(sid, using=None):
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"""
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Commits the most recent savepoint (if one exists). Does nothing if
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savepoints are not supported.
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"""
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get_connection(using).savepoint_commit(sid)
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def clean_savepoints(using=None):
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"""
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Resets the counter used to generate unique savepoint ids in this thread.
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"""
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get_connection(using).clean_savepoints()
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def get_rollback(using=None):
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"""
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Gets the "needs rollback" flag -- for *advanced use* only.
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"""
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return get_connection(using).get_rollback()
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def set_rollback(rollback, using=None):
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"""
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Sets or unsets the "needs rollback" flag -- for *advanced use* only.
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When `rollback` is `True`, it triggers a rollback when exiting the
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innermost enclosing atomic block that has `savepoint=True` (that's the
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default). Use this to force a rollback without raising an exception.
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When `rollback` is `False`, it prevents such a rollback. Use this only
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after rolling back to a known-good state! Otherwise, you break the atomic
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block and data corruption may occur.
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"""
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return get_connection(using).set_rollback(rollback)
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#################################
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# Decorators / context managers #
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#################################
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class Atomic(object):
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"""
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This class guarantees the atomic execution of a given block.
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An instance can be used either as a decorator or as a context manager.
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When it's used as a decorator, __call__ wraps the execution of the
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decorated function in the instance itself, used as a context manager.
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When it's used as a context manager, __enter__ creates a transaction or a
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savepoint, depending on whether a transaction is already in progress, and
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__exit__ commits the transaction or releases the savepoint on normal exit,
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and rolls back the transaction or to the savepoint on exceptions.
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It's possible to disable the creation of savepoints if the goal is to
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ensure that some code runs within a transaction without creating overhead.
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A stack of savepoints identifiers is maintained as an attribute of the
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connection. None denotes the absence of a savepoint.
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This allows reentrancy even if the same AtomicWrapper is reused. For
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example, it's possible to define `oa = @atomic('other')` and use `@oa` or
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`with oa:` multiple times.
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Since database connections are thread-local, this is thread-safe.
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This is a private API.
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"""
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def __init__(self, using, savepoint):
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self.using = using
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self.savepoint = savepoint
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def __enter__(self):
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connection = get_connection(self.using)
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if not connection.in_atomic_block:
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# Reset state when entering an outermost atomic block.
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connection.commit_on_exit = True
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connection.needs_rollback = False
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if not connection.get_autocommit():
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# Some database adapters (namely sqlite3) don't handle
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# transactions and savepoints properly when autocommit is off.
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# Turning autocommit back on isn't an option; it would trigger
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# a premature commit. Give up if that happens.
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if connection.features.autocommits_when_autocommit_is_off:
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raise TransactionManagementError(
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"Your database backend doesn't behave properly when "
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"autocommit is off. Turn it on before using 'atomic'.")
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# When entering an atomic block with autocommit turned off,
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# Django should only use savepoints and shouldn't commit.
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# This requires at least a savepoint for the outermost block.
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if not self.savepoint:
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raise TransactionManagementError(
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"The outermost 'atomic' block cannot use "
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"savepoint = False when autocommit is off.")
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# Pretend we're already in an atomic block to bypass the code
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# that disables autocommit to enter a transaction, and make a
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# note to deal with this case in __exit__.
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connection.in_atomic_block = True
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connection.commit_on_exit = False
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if connection.in_atomic_block:
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# We're already in a transaction; create a savepoint, unless we
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# were told not to or we're already waiting for a rollback. The
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# second condition avoids creating useless savepoints and prevents
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# overwriting needs_rollback until the rollback is performed.
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if self.savepoint and not connection.needs_rollback:
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sid = connection.savepoint()
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connection.savepoint_ids.append(sid)
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else:
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connection.savepoint_ids.append(None)
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else:
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# We aren't in a transaction yet; create one.
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# The usual way to start a transaction is to turn autocommit off.
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# However, some database adapters (namely sqlite3) don't handle
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# transactions and savepoints properly when autocommit is off.
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# In such cases, start an explicit transaction instead, which has
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# the side-effect of disabling autocommit.
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if connection.features.autocommits_when_autocommit_is_off:
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connection._start_transaction_under_autocommit()
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connection.autocommit = False
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else:
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connection.set_autocommit(False)
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connection.in_atomic_block = True
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def __exit__(self, exc_type, exc_value, traceback):
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connection = get_connection(self.using)
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if connection.savepoint_ids:
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sid = connection.savepoint_ids.pop()
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else:
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# Prematurely unset this flag to allow using commit or rollback.
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connection.in_atomic_block = False
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try:
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if connection.closed_in_transaction:
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# The database will perform a rollback by itself.
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# Wait until we exit the outermost block.
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pass
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elif exc_type is None and not connection.needs_rollback:
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if connection.in_atomic_block:
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# Release savepoint if there is one
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if sid is not None:
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try:
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connection.savepoint_commit(sid)
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except DatabaseError:
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try:
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connection.savepoint_rollback(sid)
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except Error:
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# If rolling back to a savepoint fails, mark for
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# rollback at a higher level and avoid shadowing
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# the original exception.
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connection.needs_rollback = True
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raise
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else:
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# Commit transaction
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try:
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connection.commit()
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except DatabaseError:
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try:
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connection.rollback()
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except Error:
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# An error during rollback means that something
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# went wrong with the connection. Drop it.
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connection.close()
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raise
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else:
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# This flag will be set to True again if there isn't a savepoint
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# allowing to perform the rollback at this level.
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connection.needs_rollback = False
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if connection.in_atomic_block:
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# Roll back to savepoint if there is one, mark for rollback
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# otherwise.
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if sid is None:
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connection.needs_rollback = True
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else:
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try:
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connection.savepoint_rollback(sid)
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except Error:
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# If rolling back to a savepoint fails, mark for
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# rollback at a higher level and avoid shadowing
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# the original exception.
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connection.needs_rollback = True
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else:
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# Roll back transaction
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try:
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connection.rollback()
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except Error:
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# An error during rollback means that something
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# went wrong with the connection. Drop it.
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connection.close()
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finally:
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# Outermost block exit when autocommit was enabled.
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if not connection.in_atomic_block:
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if connection.closed_in_transaction:
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connection.connection = None
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elif connection.features.autocommits_when_autocommit_is_off:
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connection.autocommit = True
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else:
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connection.set_autocommit(True)
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# Outermost block exit when autocommit was disabled.
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elif not connection.savepoint_ids and not connection.commit_on_exit:
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if connection.closed_in_transaction:
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connection.connection = None
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else:
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connection.in_atomic_block = False
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def __call__(self, func):
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@wraps(func, assigned=available_attrs(func))
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def inner(*args, **kwargs):
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with self:
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return func(*args, **kwargs)
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return inner
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def atomic(using=None, savepoint=True):
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# Bare decorator: @atomic -- although the first argument is called
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# `using`, it's actually the function being decorated.
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if callable(using):
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return Atomic(DEFAULT_DB_ALIAS, savepoint)(using)
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# Decorator: @atomic(...) or context manager: with atomic(...): ...
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else:
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return Atomic(using, savepoint)
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def _non_atomic_requests(view, using):
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try:
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view._non_atomic_requests.add(using)
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except AttributeError:
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view._non_atomic_requests = set([using])
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return view
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def non_atomic_requests(using=None):
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if callable(using):
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return _non_atomic_requests(using, DEFAULT_DB_ALIAS)
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else:
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if using is None:
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using = DEFAULT_DB_ALIAS
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return lambda view: _non_atomic_requests(view, using)
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