model.py

# -*- coding:utf-8 -*-
import hashlib

from sqlalchemy import create_engine, MetaData, Table, Column, types
from sqlalchemy.orm import sessionmaker, scoped_session, mapper as sqla_mapper
from sqlalchemy.orm.query import Query
from sqlalchemy.sql import visitors

from werkzeug.contrib.cache import MemcachedCache
#ToDo:
# テストコード
#  モデルを追加して，読み出す．まずキャッシュが効いてるか．次にtimeout後に
#  キャッシュが効かなくなってるか
class CacheingQuery(Query):

    _timeout = 60
    _cache_engine = None
    def use_cache(self):
        return True
        #ToDo:あとで検討したほうがいいかも

    def get_cache_engine(self):
        # CacheingQueryクラスのスコープが怪しいので注意
        if CacheingQuery._cache_engine == None:
           CacheingQuery._cache_engine = MemcachedCache(['127.0.0.1:11211'])
        return CacheingQuery._cache_engine

    def _get_cache_key(self):
        key = hashlib.md5(str(self)).hexdigest()
        args = _params_from_query(self)
        args_key = " ".join([str(x) for x in args])
        key = key + "_" + args_key
        key = key.replace(' ', '_')
        return key

    def __iter__(self):

        cache_key = self._get_cache_key()
        cache_engine = self.get_cache_engine()

        if not self.use_cache():
            cache_engine.delete(cache_key)

        ret = cache_engine.get(cache_key)
        if ret == None:
            ret = list(Query.__iter__(self))
            cache_engine.set(cache_key, ret, timeout = self._timeout)
        return iter(self.session.merge(x, dont_load=True) for x in ret)
        #return Query.__iter__(self)

def _params_from_query(query):

    v = []
    def visit_bindparam(bind):
        value = query._params.get(bind.key, bind.value)

        if callable(value):
            value = value()

        k = bind.params()
        v.append("%s:%s" % (k, value))

    for obj in query._from_obj:
        _criterion = obj.onclause
        if _criterion is not None:
            visitors.traverse(_criterion, {}, {'bindparam': visit_bindparam} )

    if query._criterion is not None:
        visitors.traverse(query._criterion, {}, {'bindparam': visit_bindparam} )
    return v

metadata = MetaData()

testmodel = Table("test", metadata,
                    Column('id', types.Integer, primary_key=True),
                    Column('name', types.Unicode(32))
                    )

class TestModel(object):
    pass

def init():
    engine = create_engine('sqlite:///:memory:', echo=True)
    session = scoped_session(sessionmaker(engine,
        autocommit = False,
        query_cls = CacheingQuery), )
    sqla_mapper(TestModel, testmodel)
    metadata.create_all(bind=engine)
    return session