example models

class User (db.model):
  name = db.StringProperty ()
  prop = db.IntergerPeroperty ()

class Presence (db.model):
  user = db.ReferenceProperty (User)
  last = db.DateTimeProperty ()

# Keys users onlines
presences     = Presence.all ().filter ('last >', date_considered_connected)
users_onlines = [x.user.key() for x in presences]

# Filters
query = User.all ()
query.filter ('prop1', 1)

# Users online and filtered
users = [x for x in query if query.key () in users_onlines]