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"""defines different strategies for creating new instances of sql.Engine.
by default there are two, one which is the "thread-local" strategy, one which is the "plain" strategy.
new strategies can be added via constructing a new EngineStrategy object which will add itself to the
list of available strategies here, or replace one of the existing name.
this can be accomplished via a mod; see the sqlalchemy/mods package for details."""
from sqlalchemy.engine import base, default, threadlocal, url
strategies = {}
class EngineStrategy(object):
"""defines a function that receives input arguments and produces an instance of sql.Engine, typically
an instance sqlalchemy.engine.base.Engine or a subclass."""
def __init__(self, name):
"""construct a new EngineStrategy object and sets it in the list of available strategies
under this name."""
self.name = name
strategies[self.name] = self
def create(self, *args, **kwargs):
"""given arguments, returns a new sql.Engine instance."""
raise NotImplementedError()
class DefaultEngineStrategy(EngineStrategy):
def create(self, name_or_url, **kwargs):
u = url.make_url(name_or_url)
module = u.get_module()
dialect = module.dialect(**kwargs)
poolargs = {}
for key in (('echo_pool', 'echo'), ('pool_size', 'pool_size'), ('max_overflow', 'max_overflow'), ('poolclass', 'poolclass'), ('pool_timeout','timeout'), ('pool', 'pool'), ('pool_recycle','recycle'),('connect_args', 'connect_args'), ('creator', 'creator')):
if kwargs.has_key(key[0]):
poolargs[key[1]] = kwargs[key[0]]
poolclass = getattr(module, 'poolclass', None)
if poolclass is not None:
poolargs.setdefault('poolclass', poolclass)
poolargs['use_threadlocal'] = self.pool_threadlocal()
provider = self.get_pool_provider(dialect, u, **poolargs)
return self.get_engine(provider, dialect, **kwargs)
def pool_threadlocal(self):
raise NotImplementedError()
def get_pool_provider(self, dialect, url, **kwargs):
raise NotImplementedError()
def get_engine(self, provider, dialect, **kwargs):
raise NotImplementedError()
class PlainEngineStrategy(DefaultEngineStrategy):
def __init__(self):
DefaultEngineStrategy.__init__(self, 'plain')
def pool_threadlocal(self):
return False
def get_pool_provider(self, dialect, url, **poolargs):
return default.PoolConnectionProvider(dialect, url, **poolargs)
def get_engine(self, provider, dialect, **kwargs):
return base.Engine(provider, dialect, **kwargs)
PlainEngineStrategy()
class ThreadLocalEngineStrategy(DefaultEngineStrategy):
def __init__(self):
DefaultEngineStrategy.__init__(self, 'threadlocal')
def pool_threadlocal(self):
return True
def get_pool_provider(self, dialect, url, **poolargs):
return threadlocal.TLocalConnectionProvider(dialect, url, **poolargs)
def get_engine(self, provider, dialect, **kwargs):
return threadlocal.TLEngine(provider, dialect, **kwargs)
ThreadLocalEngineStrategy()
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