def METHOD_NAME(self):
    super().METHOD_NAME()
    # If the Cluster is assigned to a Site, verify that all host Devices belong to that Site.
    if self.pk and self.site:
        nonsite_devices = Device.objects.filter(cluster=self).exclude(site=self.site).count()
        if nonsite_devices:
            raise ValidationError({
                'site': _("{} devices are assigned as hosts for this cluster but are not in site {}").format(
                    nonsite_devices, self.site
                )
            })