def delete_role(role_id):
''' delete a Role as long as it is not Present in a Place '''
if len(Presence.query(Presence.role == db.Key(urlsafe=role_id)).fetch()) > 0:
raise ActionException('Role still has presence')
db.Key(urlsafe=role_id).delete()
def _get_presences(place_id):
place = db.Key(urlsafe=place_id)
return [presence for presence in Presence.query(ancestor=place).fetch()]