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caching_query.py
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# -*- coding: utf-8 -*-
# Copyright (C) 2010-2017 RhodeCode GmbH
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License, version 3
# (only), as published by the Free Software Foundation.
#
# This program 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 Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
#
# This program is dual-licensed. If you wish to learn more about the
# RhodeCode Enterprise Edition, including its added features, Support services,
# and proprietary license terms, please see https://rhodecode.com/licenses/
"""
caching_query.py
Represent persistence structures which allow the usage of
Beaker caching with SQLAlchemy.
The three new concepts introduced here are:
* CachingQuery - a Query subclass that caches and
retrieves results in/from Beaker.
* FromCache - a query option that establishes caching
parameters on a Query
* RelationshipCache - a variant of FromCache which is specific
to a query invoked during a lazy load.
* _params_from_query - extracts value parameters from
a Query.
The rest of what's here are standard SQLAlchemy and
Beaker constructs.
"""
import beaker
from beaker.exceptions import BeakerException
from sqlalchemy.orm.interfaces import MapperOption
from sqlalchemy.orm.query import Query
from sqlalchemy.sql import visitors
from rhodecode.lib.utils2 import safe_str
class CachingQuery(Query):
"""A Query subclass which optionally loads full results from a Beaker
cache region.
The CachingQuery stores additional state that allows it to consult
a Beaker cache before accessing the database:
* A "region", which is a cache region argument passed to a
Beaker CacheManager, specifies a particular cache configuration
(including backend implementation, expiration times, etc.)
* A "namespace", which is a qualifying name that identifies a
group of keys within the cache. A query that filters on a name
might use the name "by_name", a query that filters on a date range
to a joined table might use the name "related_date_range".
When the above state is present, a Beaker cache is retrieved.
The "namespace" name is first concatenated with
a string composed of the individual entities and columns the Query
requests, i.e. such as ``Query(User.id, User.name)``.
The Beaker cache is then loaded from the cache manager based
on the region and composed namespace. The key within the cache
itself is then constructed against the bind parameters specified
by this query, which are usually literals defined in the
WHERE clause.
The FromCache and RelationshipCache mapper options below represent
the "public" method of configuring this state upon the CachingQuery.
"""
def __init__(self, manager, *args, **kw):
self.cache_manager = manager
Query.__init__(self, *args, **kw)
def __iter__(self):
"""override __iter__ to pull results from Beaker
if particular attributes have been configured.
Note that this approach does *not* detach the loaded objects from
the current session. If the cache backend is an in-process cache
(like "memory") and lives beyond the scope of the current session's
transaction, those objects may be expired. The method here can be
modified to first expunge() each loaded item from the current
session before returning the list of items, so that the items
in the cache are not the same ones in the current Session.
"""
if hasattr(self, '_cache_parameters'):
return self.get_value(createfunc=lambda:
list(Query.__iter__(self)))
else:
return Query.__iter__(self)
def invalidate(self):
"""Invalidate the value represented by this Query."""
cache, cache_key = _get_cache_parameters(self)
cache.remove(cache_key)
def get_value(self, merge=True, createfunc=None):
"""Return the value from the cache for this query.
Raise KeyError if no value present and no
createfunc specified.
"""
cache, cache_key = _get_cache_parameters(self)
ret = cache.get_value(cache_key, createfunc=createfunc)
if merge:
ret = self.merge_result(ret, load=False)
return ret
def set_value(self, value):
"""Set the value in the cache for this query."""
cache, cache_key = _get_cache_parameters(self)
cache.put(cache_key, value)
def query_callable(manager, query_cls=CachingQuery):
def query(*arg, **kw):
return query_cls(manager, *arg, **kw)
return query
def get_cache_region(name, region):
if region not in beaker.cache.cache_regions:
raise BeakerException('Cache region `%s` not configured '
'Check if proper cache settings are in the .ini files' % region)
kw = beaker.cache.cache_regions[region]
return beaker.cache.Cache._get_cache(name, kw)
def _get_cache_parameters(query):
"""For a query with cache_region and cache_namespace configured,
return the correspoinding Cache instance and cache key, based
on this query's current criterion and parameter values.
"""
if not hasattr(query, '_cache_parameters'):
raise ValueError("This Query does not have caching "
"parameters configured.")
region, namespace, cache_key = query._cache_parameters
namespace = _namespace_from_query(namespace, query)
if cache_key is None:
# cache key - the value arguments from this query's parameters.
args = [safe_str(x) for x in _params_from_query(query)]
args.extend(filter(lambda k: k not in ['None', None, u'None'],
[str(query._limit), str(query._offset)]))
cache_key = " ".join(args)
if cache_key is None:
raise Exception('Cache key cannot be None')
# get cache
#cache = query.cache_manager.get_cache_region(namespace, region)
cache = get_cache_region(namespace, region)
# optional - hash the cache_key too for consistent length
# import uuid
# cache_key= str(uuid.uuid5(uuid.NAMESPACE_DNS, cache_key))
return cache, cache_key
def _namespace_from_query(namespace, query):
# cache namespace - the token handed in by the
# option + class we're querying against
namespace = " ".join([namespace] + [str(x) for x in query._entities])
# memcached wants this
namespace = namespace.replace(' ', '_')
return namespace
def _set_cache_parameters(query, region, namespace, cache_key):
if hasattr(query, '_cache_parameters'):
region, namespace, cache_key = query._cache_parameters
raise ValueError("This query is already configured "
"for region %r namespace %r" %
(region, namespace))
query._cache_parameters = region, namespace, cache_key
class FromCache(MapperOption):
"""Specifies that a Query should load results from a cache."""
propagate_to_loaders = False
def __init__(self, region, namespace, cache_key=None):
"""Construct a new FromCache.
:param region: the cache region. Should be a
region configured in the Beaker CacheManager.
:param namespace: the cache namespace. Should
be a name uniquely describing the target Query's
lexical structure.
:param cache_key: optional. A string cache key
that will serve as the key to the query. Use this
if your query has a huge amount of parameters (such
as when using in_()) which correspond more simply to
some other identifier.
"""
self.region = region
self.namespace = namespace
self.cache_key = cache_key
def process_query(self, query):
"""Process a Query during normal loading operation."""
_set_cache_parameters(query, self.region, self.namespace,
self.cache_key)
class RelationshipCache(MapperOption):
"""Specifies that a Query as called within a "lazy load"
should load results from a cache."""
propagate_to_loaders = True
def __init__(self, region, namespace, attribute):
"""Construct a new RelationshipCache.
:param region: the cache region. Should be a
region configured in the Beaker CacheManager.
:param namespace: the cache namespace. Should
be a name uniquely describing the target Query's
lexical structure.
:param attribute: A Class.attribute which
indicates a particular class relationship() whose
lazy loader should be pulled from the cache.
"""
self.region = region
self.namespace = namespace
self._relationship_options = {
(attribute.property.parent.class_, attribute.property.key): self
}
def process_query_conditionally(self, query):
"""Process a Query that is used within a lazy loader.
(the process_query_conditionally() method is a SQLAlchemy
hook invoked only within lazyload.)
"""
if query._current_path:
mapper, key = query._current_path[-2:]
for cls in mapper.class_.__mro__:
if (cls, key) in self._relationship_options:
relationship_option = \
self._relationship_options[(cls, key)]
_set_cache_parameters(
query,
relationship_option.region,
relationship_option.namespace,
None)
def and_(self, option):
"""Chain another RelationshipCache option to this one.
While many RelationshipCache objects can be specified on a single
Query separately, chaining them together allows for a more efficient
lookup during load.
"""
self._relationship_options.update(option._relationship_options)
return self
def _params_from_query(query):
"""Pull the bind parameter values from a query.
This takes into account any scalar attribute bindparam set up.
E.g. params_from_query(query.filter(Cls.foo==5).filter(Cls.bar==7)))
would return [5, 7].
"""
v = []
def visit_bindparam(bind):
if bind.key in query._params:
value = query._params[bind.key]
elif bind.callable:
# lazyloader may dig a callable in here, intended
# to late-evaluate params after autoflush is called.
# convert to a scalar value.
value = bind.callable()
else:
value = bind.value
v.append(value)
if query._criterion is not None:
visitors.traverse(query._criterion, {}, {'bindparam':visit_bindparam})
for f in query._from_obj:
visitors.traverse(f, {}, {'bindparam':visit_bindparam})
return v