26a00cadce
This adds a helper method to find the database engine in use, and then skips code we shouldn't execute if we are doing this another way. Note that this helper method could be useful for backend-specific code paths elsewhere, such as custom SQL being called or lack of StdDev() in sqlite3 out of the box. Signed-off-by: Dan McGee <dan@archlinux.org>
157 lines
5.1 KiB
Python
157 lines
5.1 KiB
Python
try:
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import cPickle as pickle
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except ImportError:
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import pickle
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from datetime import datetime
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import hashlib
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from pytz import utc
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from django.core.cache import cache
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from django.db import connections, router
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CACHE_TIMEOUT = 1800
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INVALIDATE_TIMEOUT = 10
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CACHE_LATEST_PREFIX = 'cache_latest_'
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def cache_function_key(func, args, kwargs):
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raw = [func.__name__, func.__module__, args, kwargs]
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pickled = pickle.dumps(raw, protocol=pickle.HIGHEST_PROTOCOL)
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key = hashlib.md5(pickled).hexdigest()
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return 'cache_function.' + func.__name__ + '.' + key
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def cache_function(length):
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"""
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A variant of the snippet posted by Jeff Wheeler at
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http://www.djangosnippets.org/snippets/109/
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Caches a function, using the function and its arguments as the key, and the
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return value as the value saved. It passes all arguments on to the
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function, as it should.
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The decorator itself takes a length argument, which is the number of
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seconds the cache will keep the result around.
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"""
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def decorator(func):
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def inner_func(*args, **kwargs):
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key = cache_function_key(func, args, kwargs)
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value = cache.get(key)
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if value is not None:
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return value
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else:
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result = func(*args, **kwargs)
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cache.set(key, result, length)
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return result
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return inner_func
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return decorator
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def clear_cache_function(func, args, kwargs):
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key = cache_function_key(func, args, kwargs)
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cache.delete(key)
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# utility to make a pair of django choices
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make_choice = lambda l: [(str(m), str(m)) for m in l]
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# These are in here because we would be jumping around in some import circles
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# and hoops otherwise. The only thing currently using these keys is the feed
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# caching stuff.
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def refresh_latest(**kwargs):
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'''A post_save signal handler to clear out the cached latest value for a
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given model.'''
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cache_key = CACHE_LATEST_PREFIX + kwargs['sender'].__name__
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# We could delete the value, but that could open a race condition
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# where the new data wouldn't have been committed yet by the calling
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# thread. Instead, explicitly set it to None for a short amount of time.
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# Hopefully by the time it expires we will have committed, and the cache
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# will be valid again. See "Scaling Django" by Mike Malone, slide 30.
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cache.set(cache_key, None, INVALIDATE_TIMEOUT)
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def retrieve_latest(sender, latest_by=None):
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# we could break this down based on the request url, but it would probably
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# cost us more in query time to do so.
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cache_key = CACHE_LATEST_PREFIX + sender.__name__
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latest = cache.get(cache_key)
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if latest:
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return latest
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try:
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if latest_by is None:
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latest_by = sender._meta.get_latest_by
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latest = sender.objects.values(latest_by).latest(latest_by)[latest_by]
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# Using add means "don't overwrite anything in there". What could be in
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# there is an explicit None value that our refresh signal set, which
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# means we want to avoid race condition possibilities for a bit.
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cache.add(cache_key, latest, CACHE_TIMEOUT)
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return latest
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except sender.DoesNotExist:
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pass
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return None
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def utc_now():
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'''Returns a timezone-aware UTC date representing now.'''
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return datetime.utcnow().replace(tzinfo=utc)
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def set_created_field(sender, **kwargs):
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'''This will set the 'created' field on any object to the current UTC time
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if it is unset. For use as a pre_save signal handler.'''
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obj = kwargs['instance']
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if hasattr(obj, 'created') and not obj.created:
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obj.created = utc_now()
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def database_vendor(model, mode='read'):
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if mode == 'read':
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database = router.db_for_read(model)
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elif mode == 'write':
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database = router.db_for_write(model)
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else:
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raise Exception('Invalid database mode specified')
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return connections[database].vendor
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def groupby_preserve_order(iterable, keyfunc):
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'''Take an iterable and regroup using keyfunc to determine whether items
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belong to the same group. The order of the iterable is preserved and
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similar keys do not have to be consecutive. This means the earliest
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occurrence of a given key will determine the order of the lists in the
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returned list.'''
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seen_keys = {}
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result = []
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for item in iterable:
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key = keyfunc(item)
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group = seen_keys.get(key, None)
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if group is None:
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group = []
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seen_keys[key] = group
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result.append(group)
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group.append(item)
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return result
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class PackageStandin(object):
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'''Resembles a Package object, and has a few of the same fields, but is
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really a link to a pkgbase that has no package with matching pkgname.'''
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def __init__(self, package):
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self.package = package
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self.pkgname = package.pkgbase
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def __getattr__(self, name):
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return getattr(self.package, name)
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def get_absolute_url(self):
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return '/packages/%s/%s/%s/' % (
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self.repo.name.lower(), self.arch.name, self.pkgbase)
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# vim: set ts=4 sw=4 et:
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