def extract_through_names(cls) -> Set[str]:
        """
        Extracts related fields through names which are shortcuts to through models.

        :return: set of related through fields names
        :rtype: Set
        """
        if cls._through_names is not None:
            return cls._through_names

        related_names = set()
        for name, field in cls.ormar_config.model_fields.items():
            if isinstance(field, BaseField) and field.is_through:
                related_names.add(name)

        cls._through_names = related_names
        return related_names

        Extracts related fields through names which are shortcuts to through models.

        :return: set of related through fields names
        :rtype: Set
        
ormar/models/mixins/relation_mixin.py