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68 lines
1.9 KiB
68 lines
1.9 KiB
# -*- encoding: utf-8 -*-
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from __future__ import absolute_import, unicode_literals
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import time
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from sqlalchemy.sql import select, func
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from . import Base
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class SQLite3Cache(Base):
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"""Implements cache using SQLAlchemy Core.
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JSON is used for safe serialization of python primitives.
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"""
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serialize = True
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def __init__(self, db, threshold=1024, timeout=-1):
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super(SQLite3Cache, self).__init__(threshold, timeout)
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self.db = db
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def _get(self, ns, key):
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rv = self.db.engine.execute(
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select([self.db.cache.c.value]).where(
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self.db.cache.c.key == ns + b'-' + key)).fetchone()
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if rv is None:
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raise KeyError
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return rv[0]
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def _set(self, ns, key, value):
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with self.db.transaction:
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cnt = self.db.engine.execute(
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select([func.count(self.db.cache)])).fetchone()[0]
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if cnt + 1 > self.threshold:
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self.db.engine.execute(
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self.db.cache.delete().where(
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self.db.cache.c.key.in_(select(
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[self.db.cache.c.key])
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.order_by(self.db.cache.c.time)
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.limit(1))))
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try:
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self._get(ns, key)
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except KeyError:
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insert = True
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else:
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insert = False
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if insert:
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stmt = self.db.cache.insert().values(
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key=ns + b'-' + key, value=value, time=time.time())
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else:
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stmt = self.db.cache.update().values(
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value=value, time=time.time()).where(
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self.db.cache.c.key == ns + b'-' + key)
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self.db.engine.execute(stmt)
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def _delete(self, ns, key):
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with self.db.transaction:
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self.db.engine.execute(
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self.db.cache.delete(self.db.cache.c.key == ns + b'-' + key))
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