Add django constance to thirdpart to void dependency

thirdpart/constance/backends/database/__init__.py

@@ -0,0 +1,94 @@
+from django.core.exceptions import ImproperlyConfigured
+from django.db.models.signals import post_save
+from django.core.cache import get_cache
+
+try:
+    from django.core.cache.backends.locmem import LocMemCache
+except ImportError:
+    from django.core.cache.backends.locmem import CacheClass as LocMemCache
+
+from .. import Backend
+from ... import settings
+
+
+class DatabaseBackend(Backend):
+    def __init__(self):
+        from .models import Constance
+        self._model = Constance
+        self._prefix = settings.DATABASE_PREFIX
+        self._autofill_timeout = settings.DATABASE_CACHE_AUTOFILL_TIMEOUT
+        self._autofill_cachekey = 'autofilled'
+
+        if not self._model._meta.installed:
+            raise ImproperlyConfigured(
+                "The constance.backends.database app isn't installed "
+                "correctly. Make sure it's in your INSTALLED_APPS setting.")
+
+        if settings.DATABASE_CACHE_BACKEND:
+            self._cache = get_cache(settings.DATABASE_CACHE_BACKEND)
+            if isinstance(self._cache, LocMemCache):
+                raise ImproperlyConfigured(
+                    "The CONSTANCE_DATABASE_CACHE_BACKEND setting refers to a "
+                    "subclass of Django's local-memory backend (%r). Please set "
+                    "it to a backend that supports cross-process caching."
+                    % settings.DATABASE_CACHE_BACKEND)
+        else:
+            self._cache = None
+        self.autofill()
+        # Clear simple cache.
+        post_save.connect(self.clear, sender=self._model)
+
+    def add_prefix(self, key):
+        return "%s%s" % (self._prefix, key)
+
+    def autofill(self):
+        if not self._autofill_timeout or not self._cache:
+            return
+        full_cachekey = self.add_prefix(self._autofill_cachekey)
+        if self._cache.get(full_cachekey):
+            return
+        autofill_values = {}
+        autofill_values[full_cachekey] = 1
+        for key, value in self.mget(settings.CONFIG.keys()):
+            autofill_values[self.add_prefix(key)] = value
+        self._cache.set_many(autofill_values, timeout=self._autofill_timeout)
+
+    def mget(self, keys):
+        if not keys:
+            return
+        keys = dict((self.add_prefix(key), key) for key in keys)
+        stored = self._model._default_manager.filter(key__in=keys.keys())
+        for const in stored:
+            yield keys[const.key], const.value
+
+    def get(self, key):
+        key = self.add_prefix(key)
+        if self._cache:
+            value = self._cache.get(key)
+        else:
+            value = None
+        if value is None:
+            try:
+                value = self._model._default_manager.get(key=key).value
+            except self._model.DoesNotExist:
+                pass
+            else:
+                if self._cache:
+                    self._cache.add(key, value)
+        return value
+
+    def set(self, key, value):
+        constance, created = self._model._default_manager.get_or_create(
+            key=self.add_prefix(key), defaults={'value': value}
+        )
+        if not created:
+            constance.value = value
+            constance.save()
+
+    def clear(self, sender, instance, created, **kwargs):
+        if self._cache and not created:
+            keys = [self.add_prefix(k)
+                    for k in settings.CONFIG.keys()]
+            keys.append(self.add_prefix(self._autofill_cachekey))
+            self._cache.delete_many(keys)
+            self.autofill()