NeedIndexError on a single property (Google AppEngine + Firestore)

[RohanTalip]

Please see https://stackoverflow.com/questions/50634212/needindexerror-on-a-single-property-google-appengine-firestore and googleapis/google-cloud-python#5427 (I'm not sure if this is an issue in google-cloud-python or in datastore-ndb-python).

Please let me know if you want more information added here as opposed to at those various pages.

[RohanTalip]

So, the google-cloud-python issue was closed, indicating that this is an NDB issue.

Copying the stacktrace here:

logMessage:  "An error occurred during a request.
Traceback (most recent call last):
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask/app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask/app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask_cors/extension.py", line 161, in wrapped_function
    return cors_after_request(app.make_response(f(*args, **kwargs)))
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask/app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask/app.py", line 1612, in full_dispatch_request
    rv = self.dispatch_request()
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/lib/flask/app.py", line 1598, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/auth.py", line 42, in wrapper
    return api_function(*args, **kwargs)
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/users.py", line 51, in api_list_users
    users = User.query_users()
  File "/base/data/home/apps/s~events-12275/20180531t165330.410118595690745694/model.py", line 35, in query_users
    db_objects = query.fetch()
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/utils.py", line 160, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/query.py", line 1218, in fetch
    return self.fetch_async(limit, **q_options).get_result()
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
    self.check_success()
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 427, in _help_tasklet_along
    value = gen.throw(exc.__class__, exc, tb)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/query.py", line 995, in _run_to_list
    batch = yield rpc
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 513, in _on_rpc_completion
    result = rpc.get_result()
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/api/apiproxy_stub_map.py", line 613, in get_result
    return self.__get_result_hook(self)
  File "/base/alloc/tmpfs/dynamic_runtimes/python27/277b61042b697c7a_unzipped/python27_lib/versions/1/google/appengine/datastore/datastore_query.py", line 2921, in __query_result_hook
    yaml_index=yaml, xml_index=xml)
NeedIndexError: no matching index found.
The suggested index for this query is:
- kind: User
  properties:
  - name: displayName"     
    severity:  "ERROR"

[RohanTalip]

This issue is no longer relevant for me, as I gave up on trying to use NDB for Firestore and instead used the firestore module from the Firebase admin SDK:
https://firebase.google.com/docs/admin/setup
https://firebase.google.com/docs/reference/admin/

It may still be relevant for anyone else wanting to use Firestore from GCP / App Engine though ...