Invalidate particular cache
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06-12-2019 - |
Question
I have cache tag in the base template:
{% cache 100000 categories %}
Categories output
{% endcache %}
When I add new category through Django admin, I want invalidate this cache:
class CategoriesAdmin(admin.ModelAdmin):
def save_model(self, request, obj, form, change):
super(CategoriesAdmin, self).save_model(request, obj, form, change)
cache.delete('categories')
But the cache is stay valid! What is wrong?
Solution
That's because the actual key is not "categories", but rather one that's dynamically constructed by Django using the following:
args = md5_constructor(u':'.join([urlquote(resolve_variable(var, context)) for var in self.vary_on]))
cache_key = 'template.cache.%s.%s' % (self.fragment_name, args.hexdigest())
See: https://code.djangoproject.com/browser/django/tags/releases/1.3.1/django/templatetags/cache.py
In general, the key is going to be in the format: template.cache.categories.[hexdigest]
. So the tricky part is figuring out the hexdigest part.
I found the following Django snippet (in the comments), which looks like it should still work (from 2009):
from django.core.cache import cache
from django.utils.hashcompat import md5_constructor
from django.utils.http import urlquote
def invalidate_template_cache(fragment_name, *variables):
args = md5_constructor(u':'.join([urlquote(var) for var in variables]))
cache_key = 'template.cache.%s.%s' % (fragment_name, args.hexdigest())
cache.delete(cache_key)
Since you're not passing any variables to vary on to the templatetag, you can call that with just: invalidate_template_cache('categories')
. Otherwise, you'd need to pass in a list of all the variables the template tag varies on as the second argument.
OTHER TIPS
In Django 1.6+ please use make_template_fragment_key
:
django.core.cache.utils.make_template_fragment_key(fragment_name, vary_on=None)
If you want to obtain the cache key used for a cached fragment, you can use make_template_fragment_key. fragment_name is the same as second argument to the cache template tag; vary_on is a list of all additional arguments passed to the tag. This function can be useful for invalidating or overwriting a cached item, for example:
from django.core.cache import cache
from django.core.cache.utils import make_template_fragment_key
# cache key for {% cache 500 sidebar username %}
key = make_template_fragment_key('sidebar', [username])
cache.delete(key) # invalidates cached template fragment
Works like magic :-)