In my project, I store the serial number of the device that logs in it’s session. However in the code that gets the value from the session:
SESSION_SERIAL_NUMBER = 'terminal_serial_number'
user._serial_number = request.session.get(SESSION_SERIAL_NUMBER, '')
Very occasionally throws an error. The part that baffles me is:
get() returned more than one Session – it returned more than 20!
How can a dict return more than one result, I don’t know how to debug that?
Note: When I query the database django_sessions table with the given sessionid, it only returns one row.
Heres the error:
Internal Server Error: /accounts/login/
ProgrammingError at /accounts/login/
no results to fetch
Traceback (most recent call last):
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 180, in _get_session
return self._session_cache
During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:
File "/home/company/.venv/project/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "./dist/terminals/middleware.py", line 11, in __call__
user._serial_number = request.session.get(SESSION_SERIAL_NUMBER, '')
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 65, in get
return self._session.get(key, default)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 185, in _get_session
self._session_cache = self.load()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/db.py", line 43, in load
s = self._get_session_from_db()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/db.py", line 32, in _get_session_from_db
return self.model.objects.get(
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/query.py", line 443, in get
raise self.model.MultipleObjectsReturned(
During handling of the above exception (get() returned more than one Session -- it returned more than 20!), another exception occurred:
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 180, in _get_session
return self._session_cache
During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/utils.py", line 97, in inner
return func(*args, **kwargs)
The above exception (no results to fetch) was the direct cause of the following exception:
File "/home/company/.venv/project/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/utils/deprecation.py", line 126, in __call__
response = response or self.get_response(request)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/core/handlers/exception.py", line 49, in inner
response = response_for_exception(request, exc)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/core/handlers/exception.py", line 110, in response_for_exception
response = handle_uncaught_exception(request, get_resolver(get_urlconf()), sys.exc_info())
File "/home/company/.venv/project/lib/python3.8/site-packages/django/core/handlers/exception.py", line 149, in handle_uncaught_exception
return callback(request)
File "./core/base/views.py", line 152, in error_500_view
response = render(request, "core.base/500.html", context=context)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/shortcuts.py", line 19, in render
content = loader.render_to_string(template_name, context, request, using=using)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/template/loader.py", line 62, in render_to_string
return template.render(context, request)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/template/backends/django.py", line 61, in render
return self.template.render(context)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/template/base.py", line 174, in render
with context.bind_template(self):
File "/usr/lib/python3.8/contextlib.py", line 113, in __enter__
return next(self.gen)
File "/home/company/.venv/project/lib/python3.8/site-packages/debug_toolbar/panels/templates/panel.py", line 46, in _request_context_bind_template
context = processor(self.request)
File "./core/base/context_processors.py", line 13, in project
menu = get_plug_menu(request.user)
File "./dist/plug/menu.py", line 58, in get_plug_menu
if user.is_anonymous or user.is_terminal:
File "/home/company/.venv/project/lib/python3.8/site-packages/django/utils/functional.py", line 248, in inner
self._setup()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/utils/functional.py", line 384, in _setup
self._wrapped = self._setupfunc()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/auth/middleware.py", line 25, in <lambda>
request.user = SimpleLazyObject(lambda: get_user(request))
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/auth/middleware.py", line 11, in get_user
request._cached_user = auth.get_user(request)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/auth/__init__.py", line 177, in get_user
user_id = _get_user_session_key(request)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/auth/__init__.py", line 60, in _get_user_session_key
return get_user_model()._meta.pk.to_python(request.session[SESSION_KEY])
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 50, in __getitem__
return self._session[key]
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/base.py", line 185, in _get_session
self._session_cache = self.load()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/db.py", line 43, in load
s = self._get_session_from_db()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/contrib/sessions/backends/db.py", line 32, in _get_session_from_db
return self.model.objects.get(
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/query.py", line 435, in get
num = len(clone)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/query.py", line 262, in __len__
self._fetch_all()
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/query.py", line 1354, in _fetch_all
self._result_cache = list(self._iterable_class(self))
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/query.py", line 51, in __iter__
results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1234, in execute_sql
return list(result)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1678, in cursor_iter
for rows in iter((lambda: cursor.fetchmany(itersize)), sentinel):
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1678, in <lambda>
for rows in iter((lambda: cursor.fetchmany(itersize)), sentinel):
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/utils.py", line 97, in inner
return func(*args, **kwargs)
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
raise dj_exc_value.with_traceback(traceback) from exc_value
File "/home/company/.venv/project/lib/python3.8/site-packages/django/db/utils.py", line 97, in inner
return func(*args, **kwargs)
Exception Type: ProgrammingError at /accounts/login/
Exception Value: no results to fetch
Request information:
USER: AnonymousUser
This is the middleware it sits in:
from dist.terminals.apps import SESSION_SERIAL_NUMBER
class UserSerialNumberMiddleware:
def __init__(self, get_response):
self.get_response = get_response
# One-time configuration and initialization.
def __call__(self, request):
user = request.user
user._serial_number = request.session.get(SESSION_SERIAL_NUMBER, '')
response = self.get_response(request)
return response
I thought it was a bug, and raised a ticket due to the fact its just a dictionary lookup, it seems like quite an atomic action. I suspected it must be a bug not the code, since the code is basically set a key in the session, then read the key. However the issue was closed because they don’t think its a bug. Any ideas on how t debug it or angles on how to try figure out the issue?