@michael: changed to after_commit
@ivan:
Sorry for the late reply. Here's a decent example. I have this
working in production error free, but it's hardly done. Note, the
code below is a specific example. Let me know if you have questions
from sqlalchemy import orm
def get_session_id(session):
session() # Prime session. Fails without doing this
sessions = dict((v, k) for k, v in orm.session._sessions.items())
return sessions[session]
# I put these in a class inherited by all my models. There's probably
a better way
@property
def _loaded_relations(self):
relations = set(name for name, obj in
self.__mapper__._props.iteritems()
if type(obj) is orm.properties.RelationProperty)
return relations.difference(self._sa_instance_state.unloaded)
def cache(self):
# Do not cached anything with deferred fields. That could hurt
performance and cause more db hits, not to mention I find some edge
cases where it causes errors
# Do not cached anything with loaded relations. I'm trying to fix
this. If you serialize them together, make sure to deserialize them
properly
if not self._sa_instance_state.load_options and not
self._loaded_relations:
memcache_client = get_memcache_client()
try:
serialized_instance = pickle.dumps(self)
except pickle.PickleError: # The object may include non-
serializable attributes
pass
else:
memcache_client.set(self._cache_key, serialized_instance)
@classmethod
def find_by_id(cls, id, session=SESSION): # I actually abstract this
a bit for different primary keys and unique fields, but it's a good
example
key = cls.get_cache_key(id)
memcache_client = get_memcache_client()
serialized_instance = memcache_client.get(key)
if serialized_instance is not None:
cls() # Prime model. Fails without doing this
instance = pickle.loads(serialized_instance)
instance._sa_instance_state.session_id = get_session_id
(session) # Attach to session
else:
instance = session.query(cls).filter_by(id=id).one()
instance.cache() # Serialize and store in memcache
return instance
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