[web2py] Selecting subsets of objects in a controller.

[Joe J]

Hi All,
  I have a one-to-many relationship between a table called "org" and a
table called "eventtype".  (one org can have many eventtypes).

I'm trying to construct a controller function that can edit a
eventtype belonging to a specific org.  The URL might look something
like:
/app_name/eventtype/edit/[org_name_id]/[event_type_id]/

I'm like to pass the org_id, and eventtype_id in as arguments to the
controller function and then return the given eventtype object
instance only if it belongs to the selected org.

def edit():
    # example I found in the book
    try: org=db.org(request.args(0))
    except: redirect(URL('org','index'))

    eventtype_id = request.args(1)
    # trying to find a way to select the eventtype
    # from the orgs available eventtypes.  I want
    # the eventtype var to be the selected
    # eventtype instance (not a list of fields)
    try: eventtype=db.eventtype(eventtype_id, db.org???)
    except: redirect(URL('org','index'))

If it helps clarify the question, here is the Django syntax for what I
am trying to do.
    ....
    try:
        eventtype=org.eventtype_set.get(id=eventtype_id)
    except ....
        return HttpRedirect(...)

Any help is much appreciated.  Thank you for reading at this.
Joe