Question

I am running into an error that I am unable to isolate the root cause of. The error is the following: “ReferenceProperty failed to be resolved: [u’StatusLog’, STATUSLOGSID]”. This error only occurs sometimes, about once or twice a day. The scripts that generate this error succeed way more often than they fail. The strangest thing about the error is that it is failing to resolve a reference property, which should never be the case (in regards to this situation) because the entities that are being referenced are never deleted by my webapp. Furthermore, I am not generating the keys that are being referenced, the Google App Engine is. The relevant code is listed below.

THE GAE TRANSACTION:

def updateStatus(key):
    hbo = HBO.get(key)
    hbo.updateStatus()
    hbo.put()

class HBOCRON(webapp2.RequestHandler):
    def get(self):
        keys = db.Query(HBO, keys_only = True).filter("inactive = ", False)
        XG_ON = db.create_transaction_options(xg=True)
        for key in keys: db.run_in_transaction_options(XG_ON, updateStatus, key)

app = webapp2.WSGIApplication([('/cron/hbo', HBOCRON)],debug=True)

Two other relevant functions…

def logStatus(self):
    self.status = StatusLog(
        hbo = self,
        prev = self.status,
        date = datetime.datetime.now(),
        on = self.online(),
        up = self.upToDate(),
        dns = self.DNS_update_needed,
        dis = self.manually_disabled).put()

def updateStatus(self):
    status = self.status
    if status is None \
        or status.on != self.online() \
        or status.up != self.upToDate() \
        or status.dns != self.DNS_update_needed:
        self.logStatus()
        self.flagged = True
    elif status.dis != self.manually_disabled:
        self.logStatus()

Traceback:

ReferenceProperty failed to be resolved: [u'StatusLog', 248327L]
Traceback (most recent call last):
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1511, in __call__
    rv = self.handle_exception(request, response, e)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1505, in __call__
    rv = self.router.dispatch(request, response)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1253, in default_dispatcher
    return route.handler_adapter(request, response)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 1077, in __call__
    return handler.dispatch()
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 547, in dispatch
    return self.handle_exception(e, self.app.debug)
  File "/base/python27_runtime/python27_lib/versions/third_party/webapp2-2.3/webapp2.py", line 545, in dispatch
    return method(*args, **kwargs)
  File "/base/data/home/apps/s~hs-hbo/1.357660268729453201/api/hbo/getCheckin.py", line 88, in post
    (hbo, data) = db.run_in_transaction_options(XG_ON, checkinTransaction, self.request)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/datastore.py", line 2476, in RunInTransactionOptions
    ok, result = _DoOneTry(new_connection, function, args, kwargs)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/api/datastore.py", line 2498, in _DoOneTry
    result = function(*args, **kwargs)
  File "/base/data/home/apps/s~hs-hbo/1.357660268729453201/api/hbo/getCheckin.py", line 33, in checkinTransaction
    hbo.updateStatus()
  File "/base/data/home/apps/s~hs-hbo/1.357660268729453201/shared/datastore.py", line 116, in updateStatus
    return self.logStatus()
  File "/base/data/home/apps/s~hs-hbo/1.357660268729453201/shared/datastore.py", line 102, in logStatus
    prev = self.status,
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/db/__init__.py", line 3597, in __get__
    reference_id.to_path())
ReferencePropertyResolveError: ReferenceProperty failed to be resolved: [u'StatusLog', 248327L]

Thanks for any insight/help/answers/suggestions!

Answer 1

This happens when you attempt to resolve a reference property (by dereferencing it – for instance, (MyModel.MyReferenceProp.foo), and the property being referenced no longer exists – because it has been deleted.

You need to modify your code to catch this exception when you dereference an entity that may have been deleted, and handle it appropriately.