>>> from noc.inv.models.unknownmodel import UnknownModel
>>> for um in UnknownModel.objects.filter():
...     um.delete()
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/noc/local/lib/python2.7/site-packages/mongoengine/queryset/manager.py", line 37, in __get__
    queryset = queryset_class(owner, owner._get_collection())
  File "/opt/noc/local/lib/python2.7/site-packages/mongoengine/document.py", line 198, in _get_collection
    db = cls._get_db()
  File "/opt/noc/local/lib/python2.7/site-packages/mongoengine/document.py", line 176, in _get_db
    return get_db(cls._meta.get('db_alias', DEFAULT_CONNECTION_NAME))
  File "/opt/noc/local/lib/python2.7/site-packages/mongoengine/connection.py", line 333, in get_db
    conn = get_connection(alias)
  File "/opt/noc/local/lib/python2.7/site-packages/mongoengine/connection.py", line 243, in get_connection
    raise MongoEngineConnectionError(msg)
mongoengine.connection.MongoEngineConnectionError: You have not defined a default connection