old_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  #    OpenERP, Open Source Management Solution
  #    Copyright (C) 2010 OpenERP s.a. (<http://openerp.com>).
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    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 Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  #
  ##############################################################################
  
  import openerp
  
  class osv_memory_autovacuum(openerp.osv.osv.osv_memory):
      """ Expose the osv_memory.vacuum() method to the cron jobs mechanism. """
      _name = 'osv_memory.autovacuum'
  
      def power_on(self, cr, uid, context=None):
          for model in self.pool.obj_list():
              obj = self.pool.get(model)
              if obj._transient:
                  obj.vacuum(cr, uid)
          return True
  
  
new_contents: # -*- coding: utf-8 -*-
  ##############################################################################
  #
  #    OpenERP, Open Source Management Solution
  #    Copyright (C) 2010 OpenERP s.a. (<http://openerp.com>).
  #
  #    This program is free software: you can redistribute it and/or modify
  #    it under the terms of the GNU Affero General Public License as
  #    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 Affero General Public License for more details.
  #
  #    You should have received a copy of the GNU Affero General Public License
  #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  #
  ##############################################################################
  
  import openerp
  
  class osv_memory_autovacuum(openerp.osv.osv.osv_memory):
      """ Expose the osv_memory.vacuum() method to the cron jobs mechanism. """
      _name = 'osv_memory.autovacuum'
  
      def power_on(self, cr, uid, context=None):
          for model in self.pool.obj_list():
              obj = self.pool.get(model)
              if obj.is_transient():
                  obj.vacuum(cr, uid)
          return True
  
  
subject: use the method instead of accessing the field directly.