def extract_related_names(cls) -> Set[str]:
        """
        Returns List of fields names for all relations declared on a model.
        List is cached in cls._related_names for quicker access.

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

        related_names = set()
        for name, field in cls.ormar_config.model_fields.items():
            if (
                isinstance(field, BaseField)
                and field.is_relation
                and not field.is_through
                and not field.skip_field
            ):
                related_names.add(name)
        cls._related_names = related_names

        return related_names

        Returns List of fields names for all relations declared on a model.
        List is cached in cls._related_names for quicker access.

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