Get mapping of items_ids to concepts containing these items

        Args:
            lang (str): language of concepts

        Returns:
            dict: item (int) -> set of concepts (int)

def get_item_concept_mapping(self, lang):
        """ Get mapping of items_ids to concepts containing these items

        Args:
            lang (str): language of concepts

        Returns:
            dict: item (int) -> set of concepts (int)

        """
        concepts = self.filter(active=True, lang=lang)
        return group_keys_by_value_lists(Concept.objects.get_concept_item_mapping(concepts, lang))