Factorise code a tiny bit.

This prepares for more invasive changes about cache_id computation.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@37184 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ZSQLCatalog/SQLCatalog.py

@@ -112,10 +112,11 @@ class transactional_cache_decorator:
   def __call__(self, method):
     def wrapper(wrapped_self):
       transactional_cache = getTransactionalVariable(None)
+      cache_id = self.cache_id
       try:
-        return transactional_cache[self.cache_id]
+        result = transactional_cache[cache_id]
       except KeyError:
-        result = transactional_cache[self.cache_id] = method(wrapped_self)
+        result = transactional_cache[cache_id] = method(wrapped_self)
       return result
     return wrapper