Add a cache clearing mechanism to fix rights update problems

Signed-off-by: Skia <skia@libskia.so>

core/__init__.py

@@ -22,3 +22,4 @@
 #
 #
 
+default_app_config = 'core.apps.SithConfig'

core/apps.py

@@ -0,0 +1,57 @@
+# -*- coding:utf-8 -*
+#
+# Copyright 2017
+# - Skia <skia@libskia.so>
+#
+# Ce fichier fait partie du site de l'Association des Étudiants de l'UTBM,
+# http://ae.utbm.fr.
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License a published by the Free Software
+# Foundation; either version 3 of the License, or (at your option) any later
+# version.
+#
+# 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 General Public License along with
+# this program; if not, write to the Free Sofware Foundation, Inc., 59 Temple
+# Place - Suite 330, Boston, MA 02111-1307, USA.
+#
+#
+
+from django.apps import AppConfig
+from django.dispatch import receiver
+from django.db.models.signals import pre_save, post_save, m2m_changed
+
+class SithConfig(AppConfig):
+    name = 'core'
+    verbose_name = "Core app of the Sith"
+
+    def ready(self):
+        from core.models import User, Group
+        from club.models import Club, Membership
+        from forum.models import Forum
+
+        def clear_cached_groups(sender, **kwargs):
+            if kwargs['model'] == Group:
+                User._group_ids = {}
+                User._group_name = {}
+
+        def clear_cached_memberships(sender, **kwargs):
+            User._club_memberships = {}
+            Club._memberships = {}
+            Forum._club_memberships = {}
+
+        print("Connecting signals!")
+        m2m_changed.connect(clear_cached_groups, weak=False, dispatch_uid="clear_cached_groups")
+        post_save.connect(clear_cached_memberships, weak=False, sender=Membership, # Membership is cached
+                dispatch_uid="clear_cached_memberships_membership")
+        post_save.connect(clear_cached_memberships, weak=False, sender=Club, # Club has a cache of Membership
+                dispatch_uid="clear_cached_memberships_club")
+        post_save.connect(clear_cached_memberships, weak=False, sender=Forum, # Forum has a cache of Membership
+                dispatch_uid="clear_cached_memberships_forum")
+        # TODO: there may be a need to add more cache clearing
+