cannot concatenate 'str' and 'tuple' objects - Django - johnny cache
-
30-05-2021 - |
Question
I try to install johnny cache with my django website.
So i set up all the johnny cache related settings like this:
CACHES = {
'default': {
# 'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
'LOCATION': '127.0.0.1:11211',
'BACKEND': 'johnny.backends.memcached.MemcachedCache',
'JOHNNY_CACHE': True,
}
}
So far, the whole project still run properly in production mode.
But immediatly after setting up the middlewares
'johnny.middleware.LocalStoreClearMiddleware'
and 'johnny.middleware.QueryCacheMiddleware'
I get the following exception:
Environment:
Request Method: GET
Django Version: 1.3.1
Python Version: 2.6.6
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.sites',
'django.contrib.messages',
'django.contrib.staticfiles',
'core_knowledge_platform.core_web_service',
'south']
Installed Middleware:
('johnny.middleware.LocalStoreClearMiddleware',
'django.middleware.common.CommonMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'johnny.middleware.QueryCacheMiddleware')
Traceback:
File "/usr/lib/python2.6/site-packages/django/core/handlers/base.py" in get_response
117. response = middleware_method(request, e)
File "/usr/lib/python2.6/site-packages/django/core/handlers/base.py" in get_response
111. response = callback(request, *callback_args, **callback_kwargs)
File "/u1/msc/vg55/public_html/core_knowledge_web_platform/core_knowledge_platform/core_web_service/views.py" in __call__
95. return getattr(self, method)(request, *args, **kwargs)
File "/u1/msc/vg55/public_html/core_knowledge_web_platform/core_knowledge_platform/core_web_service/views.py" in GET
673. if not access.validate_user_is_editor(request.user):
File "/u1/msc/vg55/public_html/core_knowledge_web_platform/core_knowledge_platform/core_web_service/business_logic/access.py" in validate_user_is_editor
38. if papergroups:
File "/usr/lib/python2.6/site-packages/django/db/models/query.py" in __nonzero__
113. iter(self).next()
File "/usr/lib/python2.6/site-packages/django/db/models/query.py" in _result_iter
107. self._fill_cache()
File "/usr/lib/python2.6/site-packages/django/db/models/query.py" in _fill_cache
772. self._result_cache.append(self._iter.next())
File "/usr/lib/python2.6/site-packages/django/db/models/query.py" in iterator
273. for row in compiler.results_iter():
File "/usr/lib/python2.6/site-packages/django/db/models/sql/compiler.py" in results_iter
698. row = self.resolve_columns(row, fields)
File "/usr/lib/python2.6/site-packages/django/db/backends/mysql/compiler.py" in resolve_columns
12. return row[:index_extra_select] + tuple(values)
Exception Type: TypeError at /publication/
Exception Value: cannot concatenate 'str' and 'tuple' objects
NB: johnny cache is not set in the INSTALLED_APPS as the documentation says it's useless
EDIT:
Well, I've discovered that the exception is thrown only when there is a cache hit. When I wait for the stored values in memcached to be expired, then on loading page, no exception is thrown...
To add more shadow to my issue, when I run the whole project with johnny activated in localhost, everything works out. But when I run it in prod environment (Apache/2.2.15 (CentOS)), there the exception is thrown... And django version on both environment are exactly the same: 1.3.1
NB: I've set up the middleware order as specified by okm
Thank you
Solution
I have had the exact same issue. While I am still trying to get to the exact bottom of it, I have found some useful things.
Older versions of johnny cache work. Since I need master/slave setups to work, I used this fork: https://bitbucket.org/skoczen/johnny-cache It only includes commits up to November, so the problem is introduced after that.
On the admin pages, the error is caused by the auth_user and auth_table table caches. Adding these to the JOHNNY_BLACKLIST circumvents the issue, and also disables caching for those tables. I doubt the issue is unique to those tables, so I'm blacklisting those tables is not a good solution.
I have checked my configuration and tried many things, just like you and that is not the problem.
Hope this helps.
Edit: More digging has revealed that the issue crops up with this commit bcdb46c5d357, which added code to cache queries returning null: https://bitbucket.org/jmoiron/johnny-cache/changeset/bcdb46c5d357
If you stick to an earlier one, it should work.
OTHER TIPS
Then the ordering of middlewares could be the reason of the error, try
'johnny.middleware.LocalStoreClearMiddleware',
'johnny.middleware.QueryCacheMiddleware', # Here
'django.middleware.common.CommonMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
# Probably you need this for transaction, later
# 'johnny.middleware.CommittingTransactionMiddleware',
The 'johnny.middleware.QueryCacheMiddleware'
should be initialized and thus be placed before other middlewares. 'johnny.middleware.LocalStoreClearMiddleware'
only deals w/ response and exception, thus it could be the first.