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# -*- coding: utf-8 -*-
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# Copyright (C) 2010-2018 RhodeCode GmbH
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License, version 3
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# (only), as published by the Free Software Foundation.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# This program is dual-licensed. If you wish to learn more about the
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# RhodeCode Enterprise Edition, including its added features, Support services,
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# and proprietary license terms, please see https://rhodecode.com/licenses/
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"""caching_query.py
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Represent functions and classes
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which allow the usage of Dogpile caching with SQLAlchemy.
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Introduces a query option called FromCache.
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The three new concepts introduced here are:
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* CachingQuery - a Query subclass that caches and
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retrieves results in/from dogpile.cache.
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* FromCache - a query option that establishes caching
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parameters on a Query
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* RelationshipCache - a variant of FromCache which is specific
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to a query invoked during a lazy load.
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* _params_from_query - extracts value parameters from
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a Query.
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The rest of what's here are standard SQLAlchemy and
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dogpile.cache constructs.
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"""
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from sqlalchemy.orm.interfaces import MapperOption
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from sqlalchemy.orm.query import Query
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from sqlalchemy.sql import visitors
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from dogpile.cache.api import NO_VALUE
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from rhodecode.lib.utils2 import safe_str
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class CachingQuery(Query):
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"""A Query subclass which optionally loads full results from a dogpile
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cache region.
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The CachingQuery optionally stores additional state that allows it to consult
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a dogpile.cache cache before accessing the database, in the form
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of a FromCache or RelationshipCache object. Each of these objects
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refer to the name of a :class:`dogpile.cache.Region` that's been configured
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and stored in a lookup dictionary. When such an object has associated
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itself with the CachingQuery, the corresponding :class:`dogpile.cache.Region`
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is used to locate a cached result. If none is present, then the
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Query is invoked normally, the results being cached.
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The FromCache and RelationshipCache mapper options below represent
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the "public" method of configuring this state upon the CachingQuery.
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"""
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def _get_region(self):
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from rhodecode.lib.rc_cache import region_meta
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return region_meta.dogpile_cache_regions
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def __init__(self, regions, *args, **kw):
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self.cache_regions = regions or self._get_region()
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Query.__init__(self, *args, **kw)
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def __iter__(self):
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"""override __iter__ to pull results from dogpile
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if particular attributes have been configured.
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Note that this approach does *not* detach the loaded objects from
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the current session. If the cache backend is an in-process cache
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(like "memory") and lives beyond the scope of the current session's
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transaction, those objects may be expired. The method here can be
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modified to first expunge() each loaded item from the current
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session before returning the list of items, so that the items
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in the cache are not the same ones in the current Session.
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"""
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super_ = super(CachingQuery, self)
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if hasattr(self, '_cache_region'):
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return self.get_value(createfunc=lambda: list(super_.__iter__()))
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else:
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return super_.__iter__()
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def _execute_and_instances(self, context):
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"""override _execute_and_instances to pull results from dogpile
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if the query is invoked directly from an external context.
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This method is necessary in order to maintain compatibility
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with the "baked query" system now used by default in some
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relationship loader scenarios. Note also the
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RelationshipCache._generate_cache_key method which enables
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the baked query to be used within lazy loads.
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.. versionadded:: 1.2.7
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"""
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super_ = super(CachingQuery, self)
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if context.query is not self and hasattr(self, '_cache_region'):
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# special logic called when the Query._execute_and_instances()
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# method is called directly from the baked query
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return self.get_value(
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createfunc=lambda: list(
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super_._execute_and_instances(context)
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)
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)
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else:
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return super_._execute_and_instances(context)
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def _get_cache_plus_key(self):
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"""Return a cache region plus key."""
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dogpile_region = self.cache_regions[self._cache_region.region]
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if self._cache_region.cache_key:
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key = self._cache_region.cache_key
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else:
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key = _key_from_query(self)
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return dogpile_region, key
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def invalidate(self):
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"""Invalidate the cache value represented by this Query."""
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dogpile_region, cache_key = self._get_cache_plus_key()
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dogpile_region.delete(cache_key)
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def get_value(self, merge=True, createfunc=None,
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expiration_time=None, ignore_expiration=False):
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"""Return the value from the cache for this query.
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Raise KeyError if no value present and no
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createfunc specified.
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"""
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dogpile_region, cache_key = self._get_cache_plus_key()
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# ignore_expiration means, if the value is in the cache
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# but is expired, return it anyway. This doesn't make sense
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# with createfunc, which says, if the value is expired, generate
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# a new value.
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assert not ignore_expiration or not createfunc, \
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"Can't ignore expiration and also provide createfunc"
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if ignore_expiration or not createfunc:
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cached_value = dogpile_region.get(cache_key,
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expiration_time=expiration_time,
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ignore_expiration=ignore_expiration)
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else:
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cached_value = dogpile_region.get_or_create(
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cache_key,
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createfunc,
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expiration_time=expiration_time
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)
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if cached_value is NO_VALUE:
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raise KeyError(cache_key)
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if merge:
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cached_value = self.merge_result(cached_value, load=False)
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return cached_value
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def set_value(self, value):
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"""Set the value in the cache for this query."""
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dogpile_region, cache_key = self._get_cache_plus_key()
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dogpile_region.set(cache_key, value)
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def query_callable(regions=None, query_cls=CachingQuery):
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def query(*arg, **kw):
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return query_cls(regions, *arg, **kw)
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return query
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def _key_from_query(query, qualifier=None):
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"""Given a Query, create a cache key.
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There are many approaches to this; here we use the simplest,
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which is to create an md5 hash of the text of the SQL statement,
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combined with stringified versions of all the bound parameters
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within it. There's a bit of a performance hit with
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compiling out "query.statement" here; other approaches include
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setting up an explicit cache key with a particular Query,
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then combining that with the bound parameter values.
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"""
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stmt = query.with_labels().statement
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compiled = stmt.compile()
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params = compiled.params
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# here we return the key as a long string. our "key mangler"
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# set up with the region will boil it down to an md5.
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return " ".join(
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[safe_str(compiled)] +
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[safe_str(params[k]) for k in sorted(params)])
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class FromCache(MapperOption):
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"""Specifies that a Query should load results from a cache."""
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propagate_to_loaders = False
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def __init__(self, region="sql_cache_short", cache_key=None):
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"""Construct a new FromCache.
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:param region: the cache region. Should be a
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region configured in the dictionary of dogpile
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regions.
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:param cache_key: optional. A string cache key
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that will serve as the key to the query. Use this
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if your query has a huge amount of parameters (such
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as when using in_()) which correspond more simply to
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some other identifier.
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"""
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self.region = region
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self.cache_key = cache_key
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def process_query(self, query):
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"""Process a Query during normal loading operation."""
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query._cache_region = self
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class RelationshipCache(MapperOption):
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"""Specifies that a Query as called within a "lazy load"
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should load results from a cache."""
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propagate_to_loaders = True
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def __init__(self, attribute, region="sql_cache_short", cache_key=None):
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"""Construct a new RelationshipCache.
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:param attribute: A Class.attribute which
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indicates a particular class relationship() whose
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lazy loader should be pulled from the cache.
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:param region: name of the cache region.
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:param cache_key: optional. A string cache key
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that will serve as the key to the query, bypassing
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the usual means of forming a key from the Query itself.
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"""
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self.region = region
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self.cache_key = cache_key
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self._relationship_options = {
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(attribute.property.parent.class_, attribute.property.key): self
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}
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def _generate_cache_key(self, path):
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"""Indicate to the lazy-loader strategy that a "baked" query
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may be used by returning ``None``.
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If this method is omitted, the default implementation of
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:class:`.MapperOption._generate_cache_key` takes place, which
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returns ``False`` to disable the "baked" query from being used.
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.. versionadded:: 1.2.7
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"""
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return None
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def process_query_conditionally(self, query):
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"""Process a Query that is used within a lazy loader.
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(the process_query_conditionally() method is a SQLAlchemy
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hook invoked only within lazyload.)
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"""
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if query._current_path:
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mapper, prop = query._current_path[-2:]
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key = prop.key
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for cls in mapper.class_.__mro__:
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if (cls, key) in self._relationship_options:
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relationship_option = self._relationship_options[(cls, key)]
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query._cache_region = relationship_option
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break
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def and_(self, option):
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"""Chain another RelationshipCache option to this one.
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While many RelationshipCache objects can be specified on a single
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Query separately, chaining them together allows for a more efficient
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lookup during load.
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"""
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self._relationship_options.update(option._relationship_options)
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return self
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