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Code Issues 32 Releases Wiki Activity

[multi-db] Reimplemented local proxying django.db.connection et al to be

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more clear and thread safe.


git-svn-id: http://code.djangoproject.com/svn/django/branches/multiple-db-support@3416 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Jason Pellerin 2006-07-21 21:59:17 +00:00
parent 422aadfe2a
commit e655cc3cc3
1 changed files with 104 additions and 106 deletions
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210
django/db/__init__.py
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@ -1,8 +1,10 @@
from django.conf import settings, UserSettingsHolder
from django import conf
from django.core import signals
from django.core.exceptions import ImproperlyConfigured
from django.dispatch import dispatcher
from thread import get_ident
try:
# Only exists in Python 2.4+
from threading import local
@ -15,8 +17,13 @@ __all__ = ('backend', 'connection', 'DatabaseError')
# singleton to represent the default connection in connections
_default = object()
if not settings.DATABASE_ENGINE:
settings.DATABASE_ENGINE = 'dummy'
# storage for local default connection
_local = local()
if not conf.settings.DATABASE_ENGINE:
conf.settings.DATABASE_ENGINE = 'dummy'
def connect(settings):
"""Connect to the database specified in settings. Returns a
@ -44,7 +51,7 @@ class ConnectionInfo(object):
"""
def __init__(self, settings=None):
if settings is None:
from django.conf import settings
settings = conf.settings
self.settings = settings
self.backend = self.load_backend()
self.connection = self.backend.DatabaseWrapper(settings)
@ -83,11 +90,11 @@ class ConnectionInfo(object):
and not f.endswith('.py') \
and not f.endswith('.pyc')]
available_backends.sort()
if settings.DATABASE_ENGINE not in available_backends:
if self.settings.DATABASE_ENGINE not in available_backends:
raise ImproperlyConfigured, \
"%r isn't an available database backend. "\
"Available options are: %s" % \
(settings.DATABASE_ENGINE,
(self.settings.DATABASE_ENGINE,
", ".join(map(repr, available_backends)))
else:
# If there's some other error, this must be an error
@ -122,11 +129,15 @@ class LazyConnectionManager(object):
def __getitem__(self, k):
try:
return self.local.connections[k]
except KeyError:
except (AttributeError, KeyError):
return self.connect(k)
def __setitem__(self, k, v):
self.local.connections[k] = v
try:
self.local.connections[k] = v
except AttributeError:
# First access in thread
self.local.connections = {k: v}
def connect(self, name):
"""Return the connection with this name in
@ -135,14 +146,16 @@ class LazyConnectionManager(object):
connection (a singleton defined in django.db), then the default
connection is returned.
"""
cnx = self.local.connections
settings = conf.settings
try:
cnx = self.local.connections
except AttributeError:
cnx = self.local.connections = {}
if name in cnx:
cnx[name].close()
if name is _default:
# get the default connection from connection_info
if connection_info.local.db is None:
connection_info.init_connection()
cnx[name] = connection_info.local.db
cnx[name] = connect(conf.settings)
return cnx[name]
try:
info = settings.OTHER_DATABASES[name]
@ -156,7 +169,7 @@ class LazyConnectionManager(object):
# In settings it's a dict, but connect() needs an object:
# pass global settings so that the default connection settings
# can be defaults for the named connections.
database = UserSettingsHolder(settings)
database = conf.UserSettingsHolder(settings)
for k, v in info.items():
setattr(database, k, v)
cnx[name] = connect(database)
@ -166,82 +179,11 @@ class LazyConnectionManager(object):
self.local.connections = {}
class _proxy:
"""A lazy-initializing proxy. The proxied object is not
initialized until the first attempt to access it.
"""
def __init__(self, init_obj):
self.__dict__['_obj'] = None
self.__dict__['_init_obj'] = init_obj
def __getattr__(self, attr):
if self.__dict__['_obj'] is None:
self.__dict__['_obj'] = self.__dict__['_init_obj']()
return getattr(self.__dict__['_obj'], attr)
def __setattr__(self, attr, val):
if self.__dict__['_obj'] is None:
self.__dict__['_obj'] = self.__dict__['_init_obj']()
setattr(self.__dict__['_obj'], attr, val)
class DefaultConnectionInfoProxy(object):
"""Holder for proxy objects that will connect to the current
default connection when used. Mimics the interface of a ConnectionInfo.
"""
def __init__(self):
self.local = local()
self.local.db = None
self.connection = _proxy(self.get_connection)
self.DatabaseError = _proxy(self.get_database_error)
self.backend = _proxy(self.get_backend)
self.get_introspection_module = _proxy(self.get_introspection_module)
self.get_creation_module = _proxy(self.get_creation_module)
self.runshell = _proxy(self.get_runshell)
def init_connection(self):
from django.conf import settings
self.local.db = connect(settings)
def get_backend(self):
if self.local.db is None:
self.init_connection()
return self.local.db.backend
def get_connection(self):
if self.local.db is None:
self.init_connection()
return self.local.db.connection
def get_database_error(self):
if self.local.db is None:
self.init_connection()
return self.local.db.DatabaseError
def get_introspection_module(self):
if self.local.db is None:
self.init_connection()
return self.local.db.get_introspection_module
def get_creation_module(self):
if self.local.db is None:
self.init_connection()
return self.local.db.get_creation_module
def get_runshell(self):
if self.local.db is None:
self.init_connection()
return self.local.db.runshell
def close(self):
self.local.db = None
def model_connection_name(klass):
"""Get the connection name that a model is configured to use, with the
given settings.
current settings.
"""
settings = conf.settings
app = klass._meta.app_label
model = klass.__name__
app_model = "%s.%s" % (app, model)
@ -283,54 +225,110 @@ class ConnectionInfoDescriptor(object):
"""
def __init__(self):
self.cnx = local()
self.cnx.cache = {}
self.local = local()
self.local.cnx = {}
dispatcher.connect(self.reset, signal=signals.request_finished)
def __get__(self, instance, type=None):
if instance is None:
raise AttributeError, \
"ConnectionInfo is accessible only through an instance"
instance_connection = self.cnx.cache.get(instance, None)
try:
instance_connection = self.local.cnx.get(instance, None)
except AttributeError:
# First access in this thread
self.local.cnx = {}
instance_connection = None
if instance_connection is None:
instance_connection = self.get_connection(instance)
self.cnx.cache[instance] = instance_connection
self.local.cnx[instance] = instance_connection
return instance_connection
def __set__(self, instance, value):
self.cnx.cache[instance] = instance_connection
try:
self.local.cnx[instance] = instance_connection
except AttributeError:
# First access in thread
self.local.cnx = {instance: instance_connection}
def __delete__(self, instance):
self.reset(instance)
try:
del self.local.cnx[instance]
except (AttributeError, KeyError):
# Not stored, no need to reset
pass
def get_connection(self, instance):
return connections[model_connection_name(instance.model)]
def reset(self):
self.cnx.cache = {}
self.local.cnx = {}
class LocalizingProxy:
"""A lazy-initializing proxy. The proxied object is not
initialized until the first attempt to access it. This is used to
attach module-level properties to local storage.
"""
def __init__(self, name, storage, func, *arg, **kw):
print name, storage, func, arg
self.__name = name
self.__storage = storage
self.__func = func
self.__arg = arg
self.__kw = kw
def __getattr__(self, attr):
if attr.startswith('_LocalizingProxy'):
return self.__dict__[attr]
try:
return getattr(getattr(self.__storage, self.__name), attr)
except AttributeError:
setattr(self.__storage, self.__name, self.__func(*self.__arg,
**self.__kw))
return getattr(getattr(self.__storage, self.__name), attr)
def __setattr__(self, attr, val):
if attr.startswith('_LocalizingProxy'):
self.__dict__[attr] = val
return
try:
print self.__storage, self.__name
stor = getattr(self.__storage, self.__name)
except AttributeError:
stor = self.__func(*self.__arg)
setattr(self.__storage, self.__name, stor)
setattr(stor, attr, val)
# Backwards compatibility: establish the default connection and set the
# default connection properties at module level
connection_info = DefaultConnectionInfoProxy()
(connection, DatabaseError, backend, get_introspection_module,
get_creation_module, runshell) = (connection_info.connection,
connection_info.DatabaseError,
connection_info.backend,
connection_info.get_introspection_module,
connection_info.get_creation_module,
connection_info.runshell)
# Create a manager for named connections
connections = LazyConnectionManager()
# Backwards compatibility: establish the default connection and set the
# default connection properties at module level, using the lazy proxy so that
# each thread may have a different default connection, if so configured
connection_info = LocalizingProxy('connection_info', _local,
lambda: connections[_default])
connection = LocalizingProxy('connection', _local,
lambda: connections[_default].connection)
backend = LocalizingProxy('backend', _local,
lambda: connections[_default].backend)
DatabaseError = LocalizingProxy('DatabaseError', _local,
lambda: connections[_default].DatabaseError)
get_introspection_module = LocalizingProxy(
'get_introspection_module', _local,
lambda: connections[_default].get_introspection_module)
get_creation_module = LocalizingProxy(
'get_creation_module', _local,
lambda: connections[_default].get_creation_module)
runshell = LocalizingProxy('runshell', _local,
lambda: connections[_default].runshell)
# Reset connections on request finish, to make sure each request can
# load the correct connections for its settings
dispatcher.connect(connections.reset, signal=signals.request_finished)
# Clear the default connection on request finish also
dispatcher.connect(connection_info.close, signal=signals.request_finished)
# Register an event that rolls back all connections
# when a Django request has an exception.