Updates cache area and returns number of items updated with all
           available entries in ICachableSource

def import_source(self, CachableSource):
        """Updates cache area and returns number of items updated with all
           available entries in ICachableSource
        """
        _count = 0
        self._import_source_items_id_list = set() # used to help speed up trim()
        for item in CachableSource.items():
            self._import_source_items_id_list.add(item.getId())
            if self.cache(item):
                _count += 1
        return _count