mirror of
https://github.com/jazzband/django-constance.git
synced 2026-03-16 22:40:24 +00:00
128 lines
4.6 KiB
Python
128 lines
4.6 KiB
Python
from django.core.cache import caches
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from django.core.cache.backends.locmem import LocMemCache
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from django.core.exceptions import ImproperlyConfigured
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from django.db import IntegrityError
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from django.db import OperationalError
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from django.db import ProgrammingError
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from django.db import transaction
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from django.db.models.signals import post_save
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from constance import config
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from constance import settings
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from constance import signals
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from constance.backends import Backend
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from constance.codecs import dumps
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from constance.codecs import loads
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class DatabaseBackend(Backend):
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def __init__(self):
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from constance.models import Constance
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self._model = Constance
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self._prefix = settings.DATABASE_PREFIX
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self._autofill_timeout = settings.DATABASE_CACHE_AUTOFILL_TIMEOUT
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self._autofill_cachekey = 'autofilled'
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if self._model._meta.app_config is None:
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raise ImproperlyConfigured(
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"The constance.backends.database app isn't installed "
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"correctly. Make sure it's in your INSTALLED_APPS setting."
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)
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if settings.DATABASE_CACHE_BACKEND:
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self._cache = caches[settings.DATABASE_CACHE_BACKEND]
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if isinstance(self._cache, LocMemCache):
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raise ImproperlyConfigured(
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'The CONSTANCE_DATABASE_CACHE_BACKEND setting refers to a '
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f"subclass of Django's local-memory backend ({settings.DATABASE_CACHE_BACKEND!r}). Please "
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'set it to a backend that supports cross-process caching.'
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)
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else:
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self._cache = None
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self.autofill()
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# Clear simple cache.
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post_save.connect(self.clear, sender=self._model)
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def add_prefix(self, key):
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return f'{self._prefix}{key}'
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def autofill(self):
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if not self._autofill_timeout or not self._cache:
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return
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full_cachekey = self.add_prefix(self._autofill_cachekey)
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if self._cache.get(full_cachekey):
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return
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autofill_values = {}
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autofill_values[full_cachekey] = 1
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for key, value in self.mget(settings.CONFIG):
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autofill_values[self.add_prefix(key)] = value
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self._cache.set_many(autofill_values, timeout=self._autofill_timeout)
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def mget(self, keys):
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if not keys:
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return
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keys = {self.add_prefix(key): key for key in keys}
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try:
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stored = self._model._default_manager.filter(key__in=keys)
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for const in stored:
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yield keys[const.key], loads(const.value)
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except (OperationalError, ProgrammingError):
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pass
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def get(self, key):
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key = self.add_prefix(key)
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value = None
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if self._cache:
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value = self._cache.get(key)
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if value is None:
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self.autofill()
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value = self._cache.get(key)
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if value is None:
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match = self._model._default_manager.filter(key=key).first()
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if match:
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value = loads(match.value)
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if self._cache:
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self._cache.add(key, value)
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return value
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def set(self, key, value):
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key = self.add_prefix(key)
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created = False
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queryset = self._model._default_manager.all()
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# Set _for_write attribute as get_or_create method does
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# https://github.com/django/django/blob/2.2.11/django/db/models/query.py#L536
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queryset._for_write = True
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try:
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constance = queryset.get(key=key)
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except (OperationalError, ProgrammingError):
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# database is not created, noop
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return
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except self._model.DoesNotExist:
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try:
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with transaction.atomic(using=queryset.db):
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queryset.create(key=key, value=dumps(value))
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created = True
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except IntegrityError:
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# Allow concurrent writes
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constance = queryset.get(key=key)
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if not created:
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old_value = loads(constance.value)
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constance.value = dumps(value)
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constance.save(update_fields=['value'])
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else:
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old_value = None
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if self._cache:
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self._cache.set(key, value)
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signals.config_updated.send(sender=config, key=key, old_value=old_value, new_value=value)
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def clear(self, sender, instance, created, **kwargs):
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if self._cache and not created:
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keys = [self.add_prefix(k) for k in settings.CONFIG]
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keys.append(self.add_prefix(self._autofill_cachekey))
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self._cache.delete_many(keys)
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self.autofill()
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