"""
This module implements a transaction manager that can be used to define
transaction handling in a request or view function. It is used by transaction
control middleware and decorators.
The transaction manager can be in managed or in auto state. Auto state means the
system is using a commit-on-save strategy (actually it's more like
commit-on-change). As soon as the .save() or .delete() (or related) methods are
called, a commit is made.
Managed transactions don't do those commits, but will need some kind of manual
or implicit commits or rollbacks.
"""
try:
import thread
except ImportError:
import dummy_thread as thread
try:
from functools import wraps
except ImportError:
from django.utils.functional import wraps# Python 2.4 fallback.
fromdjango.dbconnections,DEFAULT_DB_ALIAS
from django.conf import settings
class TransactionManagementError(Exception):
"""
This exception is thrown when something bad happens with transaction
management.
"""
pass
# The states are dictionaries of dictionaries of lists. The key to the outer
# dict is the current thread, and the key to the inner dictionary is the
# connection alias and the list is handled as a stack of values.
state = {}
savepoint_state = {}
# The dirty flag is set by *_unless_managed functions to denote that the
# code under transaction management has changed things to require a
# database commit.
# This is a dictionary mapping thread to a dictionary mapping connection
# alias to a boolean.
dirty = {}
def enter_transaction_management(managed=True, using=None):
"""
Enters transaction management for a running thread. It must be balanced with
the appropriate leave_transaction_management call, since the actual state is
managed as a stack.
The state and dirty flag are carried over from the surrounding block or
from the settings, if there is no surrounding block (dirty is always false
when no current block is running).
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
thread_ident = thread.get_ident()
if thread_ident in state and state[thread_ident].get(using):
state[thread_ident][using].append(state[thread_ident][using][-1])
else:
state.setdefault(thread_ident, {})
state[thread_ident][using] = [settings.TRANSACTIONS_MANAGED]
if thread_ident not in dirty or using not in dirty[thread_ident]:
dirty.setdefault(thread_ident, {})
dirty[thread_ident][using] = False
connection._enter_transaction_management(managed)
def leave_transaction_management(using=None):
"""
Leaves transaction management for a running thread. A dirty flag is carried
over to the surrounding block, as a commit will commit all changes, even
those from outside. (Commits are on connection level.)
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
connection._leave_transaction_management(is_managed(using=using))
thread_ident = thread.get_ident()
if thread_ident in state and state[thread_ident].get(using):
del state[thread_ident][using][-1]
else:
raise TransactionManagementError("This code isn't under transaction management")
if dirty.get(thread_ident, {}).get(using, False):
rollback(using=using)
raise TransactionManagementError("Transaction managed block ended with pending COMMIT/ROLLBACK")
dirty[thread_ident][using] = False
def is_dirty(using=None):
"""
Returns True if the current transaction requires a commit for changes to
happen.
"""
if using is None:
using = DEFAULT_DB_ALIAS
return dirty.get(thread.get_ident(), {}).get(using, False)
def set_dirty(using=None):
"""
Sets a dirty flag for the current thread and code streak. This can be used
to decide in a managed block of code to decide whether there are open
changes waiting for commit.
"""
if using is None:
using = DEFAULT_DB_ALIAS
thread_ident = thread.get_ident()
if thread_ident in dirty and using in dirty[thread_ident]:
dirty[thread_ident][using] = True
else:
raise TransactionManagementError("This code isn't under transaction management")
def set_clean(using=None):
"""
Resets a dirty flag for the current thread and code streak. This can be used
to decide in a managed block of code to decide whether a commit or rollback
should happen.
"""
if using is None:
using = DEFAULT_DB_ALIAS
thread_ident = thread.get_ident()
if thread_ident in dirty and using in dirty[thread_ident]:
dirty[thread_ident][using] = False
else:
raise TransactionManagementError("This code isn't under transaction management")
clean_savepoints(using=using)
def clean_savepoints(using=None):
if using is None:
using = DEFAULT_DB_ALIAS
thread_ident = thread.get_ident()
if thread_ident in savepoint_state and using in savepoint_state[thread_ident]:
del savepoint_state[thread_ident][using]
def is_managed(using=None):
"""
Checks whether the transaction manager is in manual or in auto state.
"""
if using is None:
using = DEFAULT_DB_ALIAS
thread_ident = thread.get_ident()
if thread_ident in state and using in state[thread_ident]:
if state[thread_ident][using]:
return state[thread_ident][using][-1]
return settings.TRANSACTIONS_MANAGED
def managed(flag=True, using=None):
"""
Puts the transaction manager into a manual state: managed transactions have
to be committed explicitly by the user. If you switch off transaction
management and there is a pending commit/rollback, the data will be
commited.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
thread_ident = thread.get_ident()
top = state.get(thread_ident, {}).get(using, None)
if top:
top[-1] = flag
if not flag and is_dirty(using=using):
connection._commit()
set_clean(using=using)
else:
raise TransactionManagementError("This code isn't under transaction management")
def commit_unless_managed(using=None):
"""
Commits changes if the system is not in managed transaction mode.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
if not is_managed(using=using):
connection._commit()
clean_savepoints(using=using)
else:
set_dirty(using=using)
def rollback_unless_managed(using=None):
"""
Rolls back changes if the system is not in managed transaction mode.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
if not is_managed(using=using):
connection._rollback()
else:
set_dirty(using=using)
def commit(using=None):
"""
Does the commit itself and resets the dirty flag.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
connection._commit()
set_clean(using=using)
def rollback(using=None):
"""
This function does the rollback itself and resets the dirty flag.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
connection._rollback()
set_clean(using=using)
def savepoint(using=None):
"""
Creates a savepoint (if supported and required by the backend) inside the
current transaction. Returns an identifier for the savepoint that will be
used for the subsequent rollback or commit.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
thread_ident = thread.get_ident()
if thread_ident in savepoint_state and using in savepoint_state[thread_ident]:
savepoint_state[thread_ident][using].append(None)
else:
savepoint_state.setdefault(thread_ident, {})
savepoint_state[thread_ident][using] = [None]
tid = str(thread_ident).replace('-', '')
sid = "s%s_x%d" % (tid, len(savepoint_state[thread_ident][using]))
connection._savepoint(sid)
return sid
def savepoint_rollback(sid, using=None):
"""
Rolls back the most recent savepoint (if one exists). Does nothing if
savepoints are not supported.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
thread_ident = thread.get_ident()
if thread_ident in savepoint_state and using in savepoint_state[thread_ident]:
connection._savepoint_rollback(sid)
def savepoint_commit(sid, using=None):
"""
Commits the most recent savepoint (if one exists). Does nothing if
savepoints are not supported.
"""
if using is None:
using = DEFAULT_DB_ALIAS
connection = connections[using]
thread_ident = thread.get_ident()
if thread_ident in savepoint_state and using in savepoint_state[thread_ident]:
connection._savepoint_commit(sid)
##############
# DECORATORS #
##############
def autocommit(using=None):
"""
Decorator that activates commit on save. This is Django's default behavior;
this decorator is useful if you globally activated transaction management in
your settings file and want the default behavior in some view functions.
"""
def inner_autocommit(func, db=None):
def _autocommit(*args, **kw):
try:
enter_transaction_management(managed=False, using=db)
managed(False, using=db)
return func(*args, **kw)
finally:
leave_transaction_management(using=db)
return wraps(func)(_autocommit)
# Note that although the first argument is *called* `using`, it
# may actually be a function; @autocommit and @autocommit('foo')
# are both allowed forms.
if using is None:
using = DEFAULT_DB_ALIAS
if callable(using):
return inner_autocommit(using, DEFAULT_DB_ALIAS)
return lambda func: inner_autocommit(func, using)
def commit_on_success(using=None):
"""
This decorator activates commit on response. This way, if the view function
runs successfully, a commit is made; if the viewfunc produces an exception,
a rollback is made. This is one of the most common ways to do transaction
control in web apps.
"""
def inner_commit_on_success(func, db=None):
def _commit_on_success(*args, **kw):
try:
enter_transaction_management(using=db)
managed(True, using=db)
try:
res = func(*args, **kw)
except:
# All exceptions must be handled here (even string ones).
if is_dirty(using=db):
rollback(using=db)
raise
else:
if is_dirty(using=db):
try:
commit(using=db)
except:
rollback(using=db)
raise
return res
finally:
leave_transaction_management(using=db)
return wraps(func)(_commit_on_success)
# Note that although the first argument is *called* `using`, it
# may actually be a function; @autocommit and @autocommit('foo')
# are both allowed forms.
if using is None:
using = DEFAULT_DB_ALIAS
if callable(using):
return inner_commit_on_success(using, DEFAULT_DB_ALIAS)
return lambda func: inner_commit_on_success(func, using)
def commit_manually(using=None):
"""
Decorator that activates manual transaction control. It just disables
automatic transaction control and doesn't do any commit/rollback of its
own -- it's up to the user to call the commit and rollback functions
themselves.
"""
def inner_commit_manually(func, db=None):
def _commit_manually(*args, **kw):
try:
enter_transaction_management(using=db)
managed(True, using=db)
return func(*args, **kw)
finally:
leave_transaction_management(using=db)
return wraps(func)(_commit_manually)
# Note that although the first argument is *called* `using`, it
# may actually be a function; @autocommit and @autocommit('foo')
# are both allowed forms.
if using is None:
using = DEFAULT_DB_ALIAS
if callable(using):
return inner_commit_manually(using, DEFAULT_DB_ALIAS)
return lambda func: inner_commit_manually(func, using)
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