@ForwardNodeSettings.subscribe('before_save')
def validate_circular_reference(schema, instance):
 if (instance.url and (instance.owner._id in instance.url)):
  raise ValidationValueError('Circular URL')

@ ForwardNodeSettings . subscribe ( 'before_save' ) def validate_circular_reference ( schema , instance ) : if ( instance . url and ( instance . owner . _id in instance . url ) ) : raise ValidationValueError ( 'Circular URL' )
prevent node from forwarding to itself .