Added comment to explain why / how cache should be ideally cleared.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@17614 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Form/Document/Preference.py

@@ -66,7 +66,15 @@ class Preference( Folder ):
 
   def _clearCache(self):
     """Clear caches used by methods of this preference
+
     # TODO: clear different caches according to the preference priority
+    # TODO: (XXX) currently, if one use enables / disables a cache, caches
+            for all other users are reset. This is not good for a system
+            in which users do a lot of preference validation. A better solution
+            is needed for this. But it is not easy because the concept of
+            "per user cache" has been proven to be ambiguous or useless.
+            In theory, a solution could consist in using more keys to
+            select caches or to delete "manually" certain cache keys.
     """
     portal_caches = getToolByName(self.getPortalObject(), 'portal_caches')
     portal_caches.clearCache(cache_factory_list=('erp5_ui_short',))
@@ -83,4 +91,3 @@ class Preference( Folder ):
   def disable(self):
     """Workflow method"""
     self._clearCache()
-