mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-10 19:00:25 -04:00
Mike Bayer
69 lines
1.8 KiB
Python
69 lines
1.8 KiB
Python
"""Example of caching objects in a per-session cache,
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including implicit usage of the statement and params as a key.
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"""
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from sqlalchemy.orm.query import Query
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from sqlalchemy.orm.session import Session
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class CachingQuery(Query):
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def __iter__(self):
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try:
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cache = self.session._cache
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except AttributeError:
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self.session._cache = cache = {}
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stmt = self.statement.compile()
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params = stmt.params
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params.update(self._params)
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cachekey = str(stmt) + str(params)
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try:
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ret = cache[cachekey]
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except KeyError:
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ret = list(Query.__iter__(self))
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cache[cachekey] = ret
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return iter(ret)
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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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# issue a query
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print sess.query(User).filter(User.name.in_(['u2', 'u3'])).all()
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# issue another
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print sess.query(User).filter(User.name == 'u1').all()
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# pull straight from cache
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print sess.query(User).filter(User.name.in_(['u2', 'u3'])).all()
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print sess.query(User).filter(User.name == 'u1').all()
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