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from sqlalchemy.util import ScopedRegistry
from sqlalchemy.orm import create_session, object_session, MapperExtension, EXT_CONTINUE
__all__ = ['SessionContext', 'SessionContextExt']
class SessionContext(object):
"""A simple wrapper for ``ScopedRegistry`` that provides a
`current` property which can be used to get, set, or remove the
session in the current scope.
By default this object provides thread-local scoping, which is the
default scope provided by sqlalchemy.util.ScopedRegistry.
Usage::
engine = create_engine(...)
def session_factory():
return Session(bind=engine)
context = SessionContext(session_factory)
s = context.current # get thread-local session
context.current = Session(bind=other_engine) # set current session
del context.current # discard the thread-local session (a new one will
# be created on the next call to context.current)
"""
def __init__(self, session_factory=None, scopefunc=None):
if session_factory is None:
session_factory = create_session
self.registry = ScopedRegistry(session_factory, scopefunc)
super(SessionContext, self).__init__()
def get_current(self):
return self.registry()
def set_current(self, session):
self.registry.set(session)
def del_current(self):
self.registry.clear()
current = property(get_current, set_current, del_current,
"""Property used to get/set/del the session in the current scope.""")
def _get_mapper_extension(self):
try:
return self._extension
except AttributeError:
self._extension = ext = SessionContextExt(self)
return ext
mapper_extension = property(_get_mapper_extension,
doc="""Get a mapper extension that implements `get_session` using this context.""")
class SessionContextExt(MapperExtension):
"""A mapper extension that provides sessions to a mapper using ``SessionContext``."""
def __init__(self, context):
MapperExtension.__init__(self)
self.context = context
def get_session(self):
return self.context.current
def init_instance(self, mapper, class_, instance, args, kwargs):
session = kwargs.pop('_sa_session', self.context.current)
session._save_impl(instance, entity_name=kwargs.pop('_sa_entity_name', None))
return EXT_CONTINUE
def init_failed(self, mapper, class_, instance, args, kwargs):
object_session(instance).expunge(instance)
return EXT_CONTINUE
def dispose_class(self, mapper, class_):
if hasattr(class_, '__init__') and hasattr(class_.__init__, '_oldinit'):
if class_.__init__._oldinit is not None:
class_.__init__ = class_.__init__._oldinit
else:
delattr(class_, '__init__')
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