def _add_relation(self, field: "BaseField") -> None:
        """
        Registers relation in the manager.
        Adds Relation instance under field.name.

        :param field: field with relation declaration
        :type field: BaseField
        """
        self._relations[field.name] = Relation(
            manager=self,
            type_=self._get_relation_type(field),
            field_name=field.name,
            to=field.to,
            through=getattr(field, "through", None),
        )

        Registers relation in the manager.
        Adds Relation instance under field.name.

        :param field: field with relation declaration
        :type field: BaseField
        
ormar/relations/relation_manager.py