mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-06-03 14:29:41 -04:00
Mike Bayer
72 lines
2.1 KiB
Python
72 lines
2.1 KiB
Python
"""Example of caching objects in a global cache."""
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from sqlalchemy.orm.query import Query, _generative
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from sqlalchemy.orm.session import Session
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# the cache. This would be replaced with the caching mechanism of
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# choice, i.e. LRU cache, memcached, etc.
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_cache = {}
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class CachingQuery(Query):
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# generative method to set a "cache" key. The method of "keying" the cache
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# here can be made more sophisticated, such as caching based on the query._criterion.
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@_generative()
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def with_cache_key(self, cachekey):
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self.cachekey = cachekey
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# single point of object loading is __iter__(). objects in the cache are not associated
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# with a session and are never returned directly; only merged copies.
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def __iter__(self):
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if hasattr(self, 'cachekey'):
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try:
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ret = _cache[self.cachekey]
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except KeyError:
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ret = list(Query.__iter__(self))
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for x in ret:
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self.session.expunge(x)
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_cache[self.cachekey] = ret
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return iter(self.session.merge(x, dont_load=True) for x in ret)
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else:
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return Query.__iter__(self)
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# example usage
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if __name__ == '__main__':
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from sqlalchemy import Column, create_engine, Integer, String
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from sqlalchemy.orm import sessionmaker
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from sqlalchemy.ext.declarative import declarative_base
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Session = sessionmaker(query_cls=CachingQuery)
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Base = declarative_base(engine=create_engine('sqlite://', echo=True))
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class User(Base):
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__tablename__ = 'users'
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id = Column(Integer, primary_key=True)
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name = Column(String(100))
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def __repr__(self):
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return "User(name=%r)" % self.name
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Base.metadata.create_all()
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sess = Session()
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sess.add_all(
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[User(name='u1'), User(name='u2'), User(name='u3')]
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)
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sess.commit()
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# cache two user objects
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sess.query(User).with_cache_key('u2andu3').filter(User.name.in_(['u2', 'u3'])).all()
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sess.close()
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sess = Session()
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# pull straight from cache
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print sess.query(User).with_cache_key('u2andu3').all()
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