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try:
from threading import local
except ImportError:
from sqlalchemy.util import ThreadLocal as local
from sqlalchemy import sql
from sqlalchemy.engine import create_engine
__all__ = ['BaseProxyEngine', 'AutoConnectEngine', 'ProxyEngine']
class BaseProxyEngine(sql.Engine):
"""Basis for all proxy engines."""
def get_engine(self):
raise NotImplementedError
def set_engine(self, engine):
raise NotImplementedError
engine = property(lambda s:s.get_engine(), lambda s,e:s.set_engine(e))
def execute_compiled(self, *args, **kwargs):
"""this method is required to be present as it overrides the execute_compiled present in sql.Engine"""
return self.get_engine().execute_compiled(*args, **kwargs)
def compiler(self, *args, **kwargs):
"""this method is required to be present as it overrides the compiler method present in sql.Engine"""
return self.get_engine().compiler(*args, **kwargs)
def __getattr__(self, attr):
"""provides proxying for methods that are not otherwise present on this BaseProxyEngine. Note
that methods which are present on the base class sql.Engine will *not* be proxied through this,
and must be explicit on this class."""
# call get_engine() to give subclasses a chance to change
# connection establishment behavior
e = self.get_engine()
if e is not None:
return getattr(e, attr)
raise AttributeError("No connection established in ProxyEngine: "
" no access to %s" % attr)
class AutoConnectEngine(BaseProxyEngine):
"""An SQLEngine proxy that automatically connects when necessary."""
def __init__(self, dburi, **kwargs):
BaseProxyEngine.__init__(self)
self.dburi = dburi
self.kwargs = kwargs
self._engine = None
def get_engine(self):
if self._engine is None:
if callable(self.dburi):
dburi = self.dburi()
else:
dburi = self.dburi
self._engine = create_engine(dburi, **self.kwargs)
return self._engine
class ProxyEngine(BaseProxyEngine):
"""Engine proxy for lazy and late initialization.
This engine will delegate access to a real engine set with connect().
"""
def __init__(self, **kwargs):
BaseProxyEngine.__init__(self)
# create the local storage for uri->engine map and current engine
self.storage = local()
self.kwargs = kwargs
def connect(self, *args, **kwargs):
"""Establish connection to a real engine."""
kwargs.update(self.kwargs)
if not kwargs:
key = repr(args)
else:
key = "%s, %s" % (repr(args), repr(sorted(kwargs.items())))
try:
map = self.storage.connection
except AttributeError:
self.storage.connection = {}
self.storage.engine = None
map = self.storage.connection
try:
self.storage.engine = map[key]
except KeyError:
map[key] = create_engine(*args, **kwargs)
self.storage.engine = map[key]
def get_engine(self):
if not hasattr(self.storage, 'engine') or self.storage.engine is None:
raise AttributeError("No connection established")
return self.storage.engine
def set_engine(self, engine):
self.storage.engine = engine
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