diff --git a/app/scodoc/sco_cache.py b/app/scodoc/sco_cache.py
index 1137e68db..826d662d0 100644
--- a/app/scodoc/sco_cache.py
+++ b/app/scodoc/sco_cache.py
@@ -75,7 +75,7 @@ class ScoDocCache:
 
     @classmethod
     def _get_key(cls, oid):
-        return cls.prefix + g.scodoc_dept + oid
+        return g.scodoc_dept + "_" + cls.prefix + oid
 
     @classmethod
     def get(cls, oid):
@@ -87,6 +87,14 @@ class ScoDocCache:
         """Store evaluation"""
         return CACHE.set(cls._get_key(oid), value, timeout=cls.timeout)
 
+    @classmethod
+    def get_cached(cls, oid):
+        """get cached object. Clients should use .get()
+        This function is usefull for tests, because get() may be
+        overloaded by subclasses.
+        """
+        return ScoDocCache.get(oid)
+
     @classmethod
     def delete(cls, oid):
         """Remove from cache"""
@@ -134,8 +142,11 @@ class AbsSemEtudCache(ScoDocCache):
     C'est pourquoi il expire après timeout secondes.
     Le timeout evite aussi d'éliminer explicitement ces éléments cachés lors
     des suppressions d'étudiants ou de semestres.
+    Clé: etudid + "_" + date_debut + "_" + date_fin
+    Valeur: (nb_abs, nb_abs_just)
     """
 
+    prefix = "ABSE"
     timeout = 60 * 60  # ttl 60 minutes