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data_cacher.py
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data_cacher.py
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# -*- coding: utf-8 -*-
## $Id$
## This file is part of CDS Invenio.
## Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008 CERN.
##
## CDS Invenio is free software; you can redistribute it and/or
## modify it under the terms of the GNU General Public License as
## published by the Free Software Foundation; either version 2 of the
## License, or (at your option) any later version.
##
## CDS Invenio is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with CDS Invenio; if not, write to the Free Software Foundation, Inc.,
## 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
"""Tool for caching important infos, which are slow to rebuild, but that rarely
change"""
from invenio.dbquery import run_sql, get_table_update_time
import time
class CacherError(Exception):
"""Error raised by data cacher"""
pass
class DataCacher:
""" DataCacher is an abstract cacher system, for caching informations
that are slow to retrieve but that don't change too much during time."""
def __init__(self, cache_filler, timestamp_getter):
""" @param cache_filler a function that receives the cache dictionary.
@param timestamp_getter a function that returns a timestamp for
checking if something has changed after cache creation.
"""
self.timestamp = 0
self.cache = {}
if not callable(cache_filler):
raise CacherError, "cache_filler is not callable"
self.cache_filler = cache_filler
if not callable(timestamp_getter):
raise CacherError, "timestamp_getter is not callable"
self.timestamp_getter = timestamp_getter
self.is_ok_p = True
self.create_cache()
def clear(self):
""" Clear the cache rebuilding it"""
self.create_cache()
def create_cache(self):
"""Create cache. Called on startup and used later during the search
time."""
# populate field I18 name cache:
self.cache = self.cache_filler()
self.timestamp = time.strftime("%Y-%m-%d %H:%M:%S", time.localtime())
def get_cache(self):
""" Obtain an uptodate cache."""
if self.timestamp_getter() > self.timestamp:
self.create_cache()
return self.cache
class SQLDataCacher(DataCacher):
""" SqlDataCacher is a cacher system, for caching single queries and
their results."""
def __init__(self, query, param=None, affected_tables=()):
""" @param query the query to cache
@param param its optional parameters as a tuple
@param affected_tables the list of tables queried by the query.
"""
self.query = query
self.affected_tables = affected_tables
assert(affected_tables)
def cache_filler():
"""Standard SQL filler, with results from sql query."""
return run_sql(self.query, param)
def timestamp_getter():
"""Standard timestamp getter from affected tables by query."""
return max([get_table_update_time(table)
for table in self.affected_tables])
DataCacher.__init__(self, cache_filler, timestamp_getter)

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