how to create a directory programatically

Bonjour!!

I'm trying to create a directory programatically, but i'm getting errors 
when I try to use the _setObject() method.
This is my code:

dtool = context.portal_directories

dir = ZODBDirectory( ... )

# here i assert that ZODBDirectory is created correctly

dtool._setObject(dir.getId(),dir)

When I comment _setObject method, all runs correctly. But when I 
discomment it, I get the next error:

Traceback (innermost last):

  Module ZPublisher.Publish, line 115, in publish

  Module ZPublisher.mapply, line 88, in mapply

  Module ZPublisher.Publish, line 41, in call_object

  Module Products.CMFCore.FSPythonScript, line 108, in __call__

  Module Shared.DC.Scripts.Bindings, line 311, in __call__

  Module Shared.DC.Scripts.Bindings, line 348, in _bindAndExec