Clearing specific cache in Django

问题:

I am using view caching for a django project.

It says the cache uses the URL as the key, so I'm wondering how to clear the cache of one of the keys if a user updates/deletes the object.

An example: A user posts a blog post to domain.com/post/1234/ .. If the user edits that, i'd like to delete the cached version of that URL by adding some kind of delete cache command at the end of the view that saves the edited post.

I'm using:

@cache_page(60 * 60)
def post_page(....):

If the post.id is 1234, it seems like this might work, but it's not:

def edit_post(....):
    # stuff that saves the edits
    cache.delete('/post/%s/' % post.id)
    return Http.....

回答1:

From django cache docs, it says that cache.delete('key') should be enough. So, it comes to my mind two problems you might have:

1. Your imports are not correct, remember that you have to import cache from the django.core.cache module:

   from django.core.cache import cache
   
   # ...
   cache.delete('my_url')
   

2. The key you're using is not correct (maybe it uses the full url, including "domain.com"). To check which is the exact url you can go into your shell:

   $ ./manage.py shell
   >>> from django.core.cache import cache
   >>> cache.has_key('/post/1234/')
   # this will return True or False, whether the key was found or not
   # if False, keep trying until you find the correct key ...
   >>> cache.has_key('domain.com/post/1234/') # including domain.com ?
   >>> cache.has_key('www.domain.com/post/1234/') # including www.domain.com ?
   >>> cache.has_key('/post/1234') # without the trailing / ?
   

回答2:

I make a function to delete key starting with some text. This help me to delete dynamic keys.

list posts cached

def get_posts(tag, page=1):
    cached_data = cache.get('list_posts_home_tag%s_page%s' % (tag, page))
    if not cached_data:
        cached_data = mycontroller.get_posts(tag, page)
        cache.set('list_posts_home_tag%s_page%s' % (tag, page), cached_data, 60)
    return cached_data

when update any post, call flush_cache

def update(data):
    response = mycontroller.update(data)
    flush_cache('list_posts_home')
    return response

flush_cache to delete any dynamic cache

def flush_cache(text):
    for key in list(cache._cache.keys()):
        if text in key:
            cache.delete(key.replace(':1:', ''))

Do not forget to import cache from django

from django.core.cache import cache