def METHOD_NAME(self, service):
    """Either set or delete the external integration link between the
    service and the storage integration.
    """
    mirror_integration_id = flask.request.form.get('mirror_integration_id')
    # If no storage integration was selected, then delete the existing
    # external integration link.
    current_integration_link, ignore = get_one_or_create(
        self._db, ExternalIntegrationLink,
        library_id=None,
        external_integration_id=service.id,
        purpose=ExternalIntegrationLink.MARC
    )
    if mirror_integration_id == self.NO_MIRROR_INTEGRATION:
        if current_integration_link:
            self._db.delete(current_integration_link)
    else:
        storage_integration = get_one(
            self._db, ExternalIntegration, id=mirror_integration_id
        )
        # Only get storage integrations that have a MARC file option set
        if not storage_integration or \
                not storage_integration.setting(S3UploaderConfiguration.MARC_BUCKET_KEY).value:
            return MISSING_INTEGRATION
        current_integration_link.other_integration_id=storage_integration.id