Hi One thing that may not be obviouse with back references (reference sets) is that if the class that holds the reference has not been imported the named collection (or entity_set) won't be available in you object that you are trying to access the back references through.
Hope that make sense. So you might have the situation where the instance has been restarted and some other code that has normally run that does the import, has yet to happen. This is probably not what is happening, but thought I would mention it. T On Feb 27, 12:21 am, Josh <[email protected]> wrote: > Hi, I'm relatively new to GAE so I'm not sure if I'm overlooking > something relatively simple, but some help would be greatly > appreciated: > > I'm working on an app where users can add others as contacts. To do > this, I have a User model and a Contact model: > > class User(db.Model): > username = db.StringProperty(required=True) > firstname = db.StringProperty() > lastname = db.StringProperty() > email = db.EmailProperty(required=True) > address = db.PostalAddressProperty(required=False) > password = db.StringProperty(required=True) > > class Contact(db.Model): > contacter = > db.ReferenceProperty(User,required=True,collection_name='contacters') > contactee = > db.ReferenceProperty(User,required=True,collection_name='contactees') > accepted = db.BooleanProperty(required=True,default=False) > > The relationships are unidirectional, so User A (contacter) can > request User B (contactee) as a contact and User B must then accept > User A. User A now has User B added as a contact, whereas User B > doesn't see anything different. To get a list of contacts for User A, > I'm using the back-reference property. > > user = db.get(self.session['userkey']) //uses other info to get fetch > a User object > ... > contactList = [] //blank array of contacts > if hasattr(user,'contacters'): > for contact in user.contacters: //loops through all Contact objects > that refer to the current user as a contacter > if contact.accepted == True: > contactList.append(contact.contactee) > > The rest of the code is arbitrary, but in short I then loop through > the contactList array and print out the users for the "contacts" page. > The problem here is that it only works sporadically. Quite > astonishingly, I sometimes refresh the page and the contacts it finds > will disappear completely. There aren't any errors being logged, and > when I come back the next day or a few hours later it's back again. I > have an autocomplete script on a different page that queries another > class to get a list of matching contacts. It uses a similar back- > reference property, and this also works sporadically. > > Are there any known issues / caching-features that I'm not aware of, > that might be causing this? Are back-references not the right way to > go about this? Thanks in advance! -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
