memcached is nice and framework-agnostic, and you just have to write a bit of code to interact with it. The general idea of memcached is:
object = try_memcached()
if not object:
object = real_query()
put_in_memcached(object)
That will likely be done in your SQLAlchemy abstraction, in your case. Since I'm unfamiliar with your entire platform (and only memcached), I did a bit of Googling.
This blogger appears to have implemented them together, and has helpfully provided a link to the code he uses. The relevant code appears to be this, which might make sense to you:
#!/usr/bin/python
"""
memcached objects for use with SQLAlchemy
"""
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see .
import memcache
import sqlalchemy
import sqlalchemy.orm
SQLA_SESSION = sqlalchemy.orm.sessionmaker()
MEMCACHED_CLIENT = memcache.Client(['127.0.0.1:11211'])
class DetachedORMObject(object):
"""
Session-detached object for use with ORM Mapping. As the SQLAlchemy
documentation indicates, creating and closing a session is not analogous
to creating and closing a database connection. Connections are pooled by
the database engine by default. Creating new sessions is of a minimal
cost. Also, objects using this wrapper will not likely interact in with
the database through the full power of SQLAlchemy queries.
"""
@classmethod
def fetch_by_field(cls, field, value):
"""Fetch a mapped orm object with the give field and value"""
session = SQLA_SESSION()
try:
class_object = session.query(cls).filter(field == value).one()
except sqlalchemy.orm.exc.NoResultFound:
class_object = None
finally:
session.close()
return class_object
def update(self):
"""Update the database with the values of the object"""
session = SQLA_SESSION()
session.add(self)
session.commit()
session.refresh(self)
session.close()
def refresh(self):
"""Refresh the object with the values of the database"""
session = SQLA_SESSION()
session.add(self)
session.refresh(self)
session.close()
def delete(self):
"""Delete the object from the database"""
session = SQLA_SESSION()
session.add(self)
session.delete(self)
session.commit()
session.close()
class MemcachedObject(object):
"""
Object Wrapper for serializing objects in memcached. Utilizes an abstract
method, get_isntance_key, to understand how to get and set objects that
impliment this class.
"""
@classmethod
def get_cached_instance(cls, instance_key):
"""Retrieve and return the object matching the instance_key"""
key = str(cls.__module__ + '.' + cls.__name__ + ':' \
+ str(instance_key))
print "Memcached Getting:", key
return MEMCACHED_CLIENT.get(key)
def set_cached_instance(self, time=0, min_compress_len=0):
"""Set the cached instance of an object"""
print "Memcached Setting:", self.get_cache_key()
return MEMCACHED_CLIENT.set(self.get_cache_key(), self, time, \
min_compress_len)
def delete_cached_instance(self, time=0):
"""Wrapper for the memcached delete method"""
print "Memcached Deleting:", self.get_cache_key()
return MEMCACHED_CLIENT.delete(self.get_cache_key(), time)
def get_cache_key(self):
"""Prepends the full class path of the object to the instance key"""
return self.__class__.__module__ + '.' + \
self.__class__.__name__ + ':' + self.get_instance_key()
def get_instance_key(self):
"""Get the instance key, must be implemented by child objects"""
raise NotImplementedError \
("'GetInstanceKey' method has not been defined.")
class MemcachedORMObject(DetachedORMObject, MemcachedObject):
"""
Putting it all together now. Implements both of the above classes. Worth
noting is the method for checking to see if the fetch_by_field method is
invoked using a primary key of the class. The same technique is used to
generate an instance key for an instance of the class.
"""
@classmethod
def fetch_by_field(cls, field, value):
"""Fetch the requested object from the cache and database"""
orm_object = None
matched_primary_key = True
for key in cls._sa_class_manager.mapper.primary_key:
if field.key != key.key:
matched_primary_key = False
if matched_primary_key:
orm_object = cls.get_cached_instance('(' + str(value) + ')')
if orm_object is None:
orm_object = super(MemcachedORMObject, cls). \
fetch_by_field(field, value)
if orm_object is not None:
orm_object.set_cached_instance()
return orm_object
def update(self):
"""Update the object in the database and memcached"""
DetachedORMObject.update(self)
self.set_cached_instance()
def refresh(self):
"""Refresh the object from the database and memcached"""
DetachedORMObject.refresh(self)
self.set_cached_instance()
def delete(self):
"""Delete the object from the database and memcached"""
DetachedORMObject.delete(self)
self.delete_cached_instance()
def get_instance_key(self):
"""Get the instance key, implimenting abstract method in base"""
key = []
for column in self._sa_instance_state.manager.mapper.primary_key:
key.append('(' + str(getattr(self, column.key)) + ')')
return ''.join(key)
Not sure if that helps, but there you have it. You can see that memcached idiom in use:
if matched_primary_key:
orm_object = cls.get_cached_instance('(' + str(value) + ')')
if orm_object is None:
orm_object = super(MemcachedORMObject, cls). \
fetch_by_field(field, value)
加载中...