[Django]-How to clear the whole cache when using django's page_cache decorator?

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32👍

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I’ve had this problem with an SQLite database cache – the clear() method doesn’t clear the cache although it works fine with a MySQL database cache. It seems that a SQLite cache needs a call to django.db.transation.commit_unless_managed() after the DELETE from [table] statement is run.

I have been using multiple caches since before official support was added into core as part of 1.3 and so have a wrapper round several of the cache calls – including clear() – so I was able to override this method and include the commit_unless_managed(). I think I should probably log it as a bug.

Here’s the outline of the code I’m using to flush a memcache cache (the default cache in django.core.cache) and a database cache stored in the cache_table of the settings.DATABASES['cache_database'] database.

from django.db import connections, transaction
from django.core.cache import cache # This is the memcache cache.

def flush():
    # This works as advertised on the memcached cache:
    cache.clear()
    # This manually purges the SQLite cache:
    cursor = connections['cache_database'].cursor()
    cursor.execute('DELETE FROM cache_table')
    transaction.commit_unless_managed(using='cache_database')

Rather than being lazy and hard coding it the way I have it should be pretty easy to get the values from settings.CACHES and django.db.router.

👤Colonel Sponsz

6👍

It’s a bug #19896 that looks to be fixed in 1.6.

If you are using an older version doing something like the following should make the clear work as expected.

from django.db import router, transaction


def clear_cache(the_cache):
    the_cache.clear()
    # commit the transaction
    db = router.db_for_write(the_cache.cache_model_class)
    transaction.commit_unless_managed(using=db)

This just makes sure that the transaction gets committed.

👤Bran Handley

4👍

Put something into cache, then try to call cache.clear() from the manage.py shell console and then manually check database cache contents. If that works then maybe your cache.clear() is just not called when new data is found.

The easiest way to understand what is going under the hood is just to put import pdb; pdb.set_trace() to the beginning of the cache.clear() function, then run debug server and wait, then some code call this func you’ll be able to execute step-by-step its code or you’ll just see that this func is not called as your expected.

👤Stack Exchange User

0👍

You can clear cache (delete all cache values) with a custom command. *I use LocMemCache which is used by default in Django:

For example, create clearcache.py in core/management/commands/ as shown below. *Don’t forget to put __init__.py to management and commands folders and the doc explains how to create a custom command in Django:

django-project
 |-core
 |  |-settings.py
 |  └-management
 |     |-__init__.py
 |     └-commands
 |        |-__init__.py
 |        └-clearcache.py # Here
 |-my_app1
 └-my_app2

Because you put clearcache.py in core folder where settings.py is so you need to set 'core' to INSTALLED_APPS otherwise the custom command is not recognized by Django:

# "core/settings.py"

INSTALLED_APPS = [
    ...
    'core', # Here
    ...
]

Then, create Command class extending BaseCommand class in core/management/commands/clearcache.py as shown below:

# "core/management/commands/clearcache.py"

from django.core.management.base import BaseCommand
from django.core.cache import cache

class Command(BaseCommand):
    def handle(self, *args, **kwargs):
        cache.clear()
        self.stdout.write('Cache is cleared\n')

Finally, running the command below can clear cache:

$ python manage.py clearcache
Cache is cleared
👤Super Kai – Kazuya Ito

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