[ADD] cache dict on the cursor, for request-local repeated reads

bzr revid: xmo@openerp.com-20120924101404-cel6oy1akabbo7id

openerp/sql_db.py

@@ -138,6 +138,16 @@ class Cursor(object):
         sure you use psycopg2 v2.4.2 or newer if you use PostgreSQL 9.1 and
         the performance hit is a concern for you.
 
+        .. attribute:: cache
+
+            Cache dictionary with a "request" (-ish) lifecycle, only lives as
+            long as the cursor itself does and proactively cleared when the
+            cursor is closed.
+
+            This cache should *only* be used to store repeatable reads as it
+            ignores rollbacks and savepoints, it should not be used to store
+            *any* data which may be modified during the life of the cursor.
+
     """
     IN_MAX = 1000 # decent limit on size of IN queries - guideline = Oracle limit
 
@@ -182,6 +192,8 @@ class Cursor(object):
 
         self._default_log_exceptions = True
 
+        self.cache = {}
+
     def __del__(self):
         if not self.__closed and not self._cnx.closed:
             # Oops. 'self' has not been closed explicitly.
@@ -279,6 +291,8 @@ class Cursor(object):
         if not self._obj:
             return
 
+        del self.cache
+
         if self.sql_log:
             self.__closer = frame_codeinfo(currentframe(),3)
         self.print_log()