code: def get_last_post_for_model(cr, uid, ids, model_pool):
      
      if type(ids) is not list:
          ids = [ids]
      res = {}
      for obj in model_pool.browse(cr, uid, ids):
          message_ids = obj.message_ids
          if message_ids:
              res[obj.id] = sorted(
                  message_ids, key=lambda x: x.date, reverse=True)[0].date
          else:
              res[obj.id] = False
      return res
docs: Given a set of ids and a model pool, return a dict of each object ids with
      their latest message date as a value.
      To be called in post-migration scripts
  
      :param cr: database cursor
      :param uid: user id, assumed to be openerp.SUPERUSER_ID
      :param ids: ids of the model in question to retrieve ids
      :param model_pool: orm model pool, assumed to be from pool.get()
      :return: a dict with ids as keys and with dates as values