310 lines
11 KiB
Python
310 lines
11 KiB
Python
from contextlib import ContextDecorator, contextmanager
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from django.db import (
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DEFAULT_DB_ALIAS, DatabaseError, Error, ProgrammingError, connections,
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)
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class TransactionManagementError(ProgrammingError):
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"""Transaction management is used improperly."""
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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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"""Get the autocommit status of the connection."""
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return get_connection(using).get_autocommit()
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def set_autocommit(autocommit, using=None):
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"""Set the autocommit status of the connection."""
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return get_connection(using).set_autocommit(autocommit)
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def commit(using=None):
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"""Commit a transaction."""
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get_connection(using).commit()
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def rollback(using=None):
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"""Roll back a transaction."""
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get_connection(using).rollback()
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def savepoint(using=None):
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"""
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Create a savepoint (if supported and required by the backend) inside the
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current transaction. Return 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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Roll back the most recent savepoint (if one exists). Do 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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Commit the most recent savepoint (if one exists). Do 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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Reset 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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"""Get the "needs rollback" flag -- for *advanced use* only."""
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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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Set or unset the "needs rollback" flag -- for *advanced use* only.
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When `rollback` is `True`, trigger a rollback when exiting the innermost
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enclosing atomic block that has `savepoint=True` (that's the default). Use
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this to force a rollback without raising an exception.
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When `rollback` is `False`, prevent such a rollback. Use this only after
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rolling back to a known-good state! Otherwise, you break the atomic block
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and data corruption may occur.
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"""
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return get_connection(using).set_rollback(rollback)
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@contextmanager
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def mark_for_rollback_on_error(using=None):
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"""
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Internal low-level utility to mark a transaction as "needs rollback" when
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an exception is raised while not enforcing the enclosed block to be in a
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transaction. This is needed by Model.save() and friends to avoid starting a
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transaction when in autocommit mode and a single query is executed.
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It's equivalent to:
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connection = get_connection(using)
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if connection.get_autocommit():
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yield
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else:
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with transaction.atomic(using=using, savepoint=False):
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yield
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but it uses low-level utilities to avoid performance overhead.
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"""
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try:
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yield
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except Exception:
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connection = get_connection(using)
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if connection.in_atomic_block:
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connection.needs_rollback = True
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raise
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def on_commit(func, using=None):
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"""
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Register `func` to be called when the current transaction is committed.
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If the current transaction is rolled back, `func` will not be called.
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"""
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get_connection(using).on_commit(func)
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#################################
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# Decorators / context managers #
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#################################
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class Atomic(ContextDecorator):
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"""
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Guarantee 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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# 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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connection.set_autocommit(False, force_begin_transaction_with_broken_autocommit=True)
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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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# The savepoint won't be reused. Release it to
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# minimize overhead for the database server.
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connection.savepoint_commit(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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# The savepoint won't be reused. Release it to
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# minimize overhead for the database server.
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connection.savepoint_commit(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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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 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 = {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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