I am trying to optimize my Django web application by leveraging browser caching. I set a Cache-Control header for max-age equal to a year in my home view function returned response. When I load up my site however, and check the response header of some of the images on my home page, the cache-control header isn't there. I tried two different methods of setting the response header. First I tried using Django's built in cache-control decorator. I also tried simply taking the rendered response, and setting the header in my view function before its return statement. Are static images cached differently ?
View Function
def view_home(request, page=None):
# FIND THE HOME PAGE IF WE DO NOT HAVE ONE
# IF NOT FOUND RETURN 404
if not page:
try:
page = WebPage.objects.get(template='home')
except WebPage.DoesNotExist:
raise Http404
try:
billboards = Billboard.get_published_objects()
except Exception as e:
logging.error(e)
billboards = None
project_types = ProjectType.get_published_objects()
budgets = Budget.get_published_objects()
deadlines = Deadline.get_published_objects()
contact_descriptions = ContactDescription.get_published_objects()
contact_form = ContactForm(type_list=project_types, budget_list=budgets,
deadline_list=deadlines, description_list=contact_descriptions)
context = {'page': page, 'billboards': billboards, 'contact_form': contact_form}
set_detail_context(request, context)
template = 'home.html'
# Add Cache control to response header
expiry_date = datetime.datetime.now() + datetime.timedelta(days=7)
response = render(request, template, context)
response['Cache-Control'] = 'max-age=602000'
response['Expires'] = expiry_date
return response
It sounds like you're setting the headers on a per-view basis. But those views are handling specific URLs, which presumably are not the URLs for your static image files. So it won't have any effect on those.
How you set the headers for your static files depends on how you're serving them.
The most straightforward solution is to use the whitenoise app. This serves static files from Django in the same way in both development and production, and has a setting to control the max-age.
If you're using an external server (e.g. ngnix or Apache) you'll need to configure it to set any custom headers. It doesn't have anything to do with Django.
If you're using the Django development server you'll have to opt out of having it handle the static files automatically, and instead use a custom view that sets the headers. (Or you could just not bother when using the development server.)
The #cache_page decorator is awesome. But for my blog I would like to keep a page in cache until someone comments on a post. This sounds like a great idea as people rarely comment so keeping the pages in memcached while nobody comments would be great. I'm thinking that someone must have had this problem before? And this is different than caching per url.
So a solution I'm thinking of is:
#cache_page( 60 * 15, "blog" );
def blog( request ) ...
And then I'd keep a list of all cache keys used for the blog view and then have way of expire the "blog" cache space. But I'm not super experienced with Django so I'm wondering if someone knows a better way of doing this?
This solution works for django versions before 1.7
Here's a solution I wrote to do just what you're talking about on some of my own projects:
def expire_view_cache(view_name, args=[], namespace=None, key_prefix=None):
"""
This function allows you to invalidate any view-level cache.
view_name: view function you wish to invalidate or it's named url pattern
args: any arguments passed to the view function
namepace: optioal, if an application namespace is needed
key prefix: for the #cache_page decorator for the function (if any)
"""
from django.core.urlresolvers import reverse
from django.http import HttpRequest
from django.utils.cache import get_cache_key
from django.core.cache import cache
# create a fake request object
request = HttpRequest()
# Loookup the request path:
if namespace:
view_name = namespace + ":" + view_name
request.path = reverse(view_name, args=args)
# get cache key, expire if the cached item exists:
key = get_cache_key(request, key_prefix=key_prefix)
if key:
if cache.get(key):
# Delete the cache entry.
#
# Note that there is a possible race condition here, as another
# process / thread may have refreshed the cache between
# the call to cache.get() above, and the cache.set(key, None)
# below. This may lead to unexpected performance problems under
# severe load.
cache.set(key, None, 0)
return True
return False
Django keys these caches of the view request, so what this does is creates a fake request object for the cached view, uses that to fetch the cache key, then expires it.
To use it in the way you're talking about, try something like:
from django.db.models.signals import post_save
from blog.models import Entry
def invalidate_blog_index(sender, **kwargs):
expire_view_cache("blog")
post_save.connect(invalidate_portfolio_index, sender=Entry)
So basically, when ever a blog Entry object is saved, invalidate_blog_index is called and the cached view is expired. NB: haven't tested this extensively, but it's worked fine for me so far.
The cache_page decorator will use CacheMiddleware in the end which will generate a cache key based on the request (look at django.utils.cache.get_cache_key) and the key_prefix ("blog" in your case). Note that "blog" is only a prefix, not the whole cache key.
You can get notified via django's post_save signal when a comment is saved, then you can try to build the cache key for the appropriate page(s) and finally say cache.delete(key).
However this requires the cache_key, which is constructed with the request for the previously cached view. This request object is not available when a comment is saved. You could construct the cache key without the proper request object, but this construction happens in a function marked as private (_generate_cache_header_key), so you are not supposed to use this function directly. However, you could build an object that has a path attribute that is the same as for the original cached view and Django wouldn't notice, but I don't recommend that.
The cache_page decorator abstracts caching quite a bit for you and makes it hard to delete a certain cache object directly. You could make up your own keys and handle them in the same way, but this requires some more programming and is not as abstract as the cache_page decorator.
You will also have to delete multiple cache objects when your comments are displayed in multiple views (i.e. index page with comment counts and individual blog entry pages).
To sum up: Django does time based expiration of cache keys for you, but custom deletion of cache keys at the right time is more tricky.
I wrote Django-groupcache for this kind of situations (you can download the code here). In your case, you could write:
from groupcache.decorators import cache_tagged_page
#cache_tagged_page("blog", 60 * 15)
def blog(request):
...
From there, you could simply do later on:
from groupcache.utils import uncache_from_tag
# Uncache all view responses tagged as "blog"
uncache_from_tag("blog")
Have a look at cache_page_against_model() as well: it's slightly more involved, but it will allow you to uncache responses automatically based on model entity changes.
With the latest version of Django(>=2.0) what you are looking for is very easy to implement:
from django.utils.cache import learn_cache_key
from django.core.cache import cache
from django.views.decorators.cache import cache_page
keys = set()
#cache_page( 60 * 15, "blog" );
def blog( request ):
response = render(request, 'template')
keys.add(learn_cache_key(request, response)
return response
def invalidate_cache()
cache.delete_many(keys)
You can register the invalidate_cache as a callback when someone updates a post in the blog via a pre_save signal.
This won't work on django 1.7; as you can see here https://docs.djangoproject.com/en/dev/releases/1.7/#cache-keys-are-now-generated-from-the-request-s-absolute-url the new cache keys are generated with the full URL, so a path-only fake request won't work. You must setup properly request host value.
fake_meta = {'HTTP_HOST':'myhost',}
request.META = fake_meta
If you have multiple domains working with the same views, you should cycle them in the HTTP_HOST, get proper key and do the clean for each one.
Django view cache invalidation for v1.7 and above. Tested on Django 1.9.
def invalidate_cache(path=''):
''' this function uses Django's caching function get_cache_key(). Since 1.7,
Django has used more variables from the request object (scheme, host,
path, and query string) in order to create the MD5 hashed part of the
cache_key. Additionally, Django will use your server's timezone and
language as properties as well. If internationalization is important to
your application, you will most likely need to adapt this function to
handle that appropriately.
'''
from django.core.cache import cache
from django.http import HttpRequest
from django.utils.cache import get_cache_key
# Bootstrap request:
# request.path should point to the view endpoint you want to invalidate
# request.META must include the correct SERVER_NAME and SERVER_PORT as django uses these in order
# to build a MD5 hashed value for the cache_key. Similarly, we need to artificially set the
# language code on the request to 'en-us' to match the initial creation of the cache_key.
# YMMV regarding the language code.
request = HttpRequest()
request.META = {'SERVER_NAME':'localhost','SERVER_PORT':8000}
request.LANGUAGE_CODE = 'en-us'
request.path = path
try:
cache_key = get_cache_key(request)
if cache_key :
if cache.has_key(cache_key):
cache.delete(cache_key)
return (True, 'successfully invalidated')
else:
return (False, 'cache_key does not exist in cache')
else:
raise ValueError('failed to create cache_key')
except (ValueError, Exception) as e:
return (False, e)
Usage:
status, message = invalidate_cache(path='/api/v1/blog/')
I had same problem and I didn't want to mess with HTTP_HOST, so I created my own cache_page decorator:
from django.core.cache import cache
def simple_cache_page(cache_timeout):
"""
Decorator for views that tries getting the page from the cache and
populates the cache if the page isn't in the cache yet.
The cache is keyed by view name and arguments.
"""
def _dec(func):
def _new_func(*args, **kwargs):
key = func.__name__
if kwargs:
key += ':' + ':'.join([kwargs[key] for key in kwargs])
response = cache.get(key)
if not response:
response = func(*args, **kwargs)
cache.set(key, response, cache_timeout)
return response
return _new_func
return _dec
To expired page cache just need to call:
cache.set('map_view:' + self.slug, None, 0)
where self.slug - param from urls.py
url(r'^map/(?P<slug>.+)$', simple_cache_page(60 * 60 * 24)(map_view), name='map'),
Django 1.11, Python 3.4.3
FWIW I had to modify mazelife's solution to get it working:
def expire_view_cache(view_name, args=[], namespace=None, key_prefix=None, method="GET"):
"""
This function allows you to invalidate any view-level cache.
view_name: view function you wish to invalidate or it's named url pattern
args: any arguments passed to the view function
namepace: optioal, if an application namespace is needed
key prefix: for the #cache_page decorator for the function (if any)
from: http://stackoverflow.com/questions/2268417/expire-a-view-cache-in-django
added: method to request to get the key generating properly
"""
from django.core.urlresolvers import reverse
from django.http import HttpRequest
from django.utils.cache import get_cache_key
from django.core.cache import cache
# create a fake request object
request = HttpRequest()
request.method = method
# Loookup the request path:
if namespace:
view_name = namespace + ":" + view_name
request.path = reverse(view_name, args=args)
# get cache key, expire if the cached item exists:
key = get_cache_key(request, key_prefix=key_prefix)
if key:
if cache.get(key):
cache.set(key, None, 0)
return True
return False
Instead of using the cache page decorator, you could manually cache the blog post object (or similar) if there are no comments, and then when there's a first comment, re-cache the blog post object so that it's up to date (assuming the object has attributes that reference any comments), but then just let that cached data for the commented blog post expire and then no bother re-cacheing...
Instead of explicit cache expiration you could probably use new "key_prefix" every time somebody comment the post. E.g. it might be datetime of the last post's comment (you could even combine this value with the Last-Modified header).
Unfortunately Django (including cache_page()) does not support dynamic "key_prefix"es (checked on Django 1.9) but there is workaround exists. You can implement your own cache_page() which may use extended CacheMiddleware with dynamic "key_prefix" support included. For example:
from django.middleware.cache import CacheMiddleware
from django.utils.decorators import decorator_from_middleware_with_args
def extended_cache_page(cache_timeout, key_prefix=None, cache=None):
return decorator_from_middleware_with_args(ExtendedCacheMiddleware)(
cache_timeout=cache_timeout,
cache_alias=cache,
key_prefix=key_prefix,
)
class ExtendedCacheMiddleware(CacheMiddleware):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if callable(self.key_prefix):
self.key_function = self.key_prefix
def key_function(self, request, *args, **kwargs):
return self.key_prefix
def get_key_prefix(self, request):
return self.key_function(
request,
*request.resolver_match.args,
**request.resolver_match.kwargs
)
def process_request(self, request):
self.key_prefix = self.get_key_prefix(request)
return super().process_request(request)
def process_response(self, request, response):
self.key_prefix = self.get_key_prefix(request)
return super().process_response(request, response)
Then in your code:
from django.utils.lru_cache import lru_cache
#lru_cache()
def last_modified(request, blog_id):
"""return fresh key_prefix"""
#extended_cache_page(60 * 15, key_prefix=last_modified)
def view_blog(request, blog_id):
"""view blog page with comments"""
Most of the solutions above didn't work in our case because we use https. The source code for get_cache_key reveals that it uses request.get_absolute_uri() to generate the cache key.
The default HttpRequest class sets the scheme as http. Thus we need to override it to use https for our dummy request object.
This is the code that works fine for us :)
from django.core.cache import cache
from django.http import HttpRequest
from django.utils.cache import get_cache_key
class HttpsRequest(HttpRequest):
#property
def scheme(self):
return "https"
def invalidate_cache_page(
path,
query_params=None,
method="GET",
):
request = HttpsRequest()
# meta information can be checked from error logs
request.META = {
"SERVER_NAME": "www.yourwebsite.com",
"SERVER_PORT": "443",
"QUERY_STRING": query_params,
}
request.path = path
key = get_cache_key(request, method=method)
if cache.has_key(key):
cache.delete(key)
Now I can use this utility function to invalidate the cache from any of our views:
page = reverse('url_name', kwargs={'id': obj.id})
invalidate_cache_page(path)
Duncan's answer works well with Django 1.9. But if we need invalidate url with GET-parameter we have to make a little changes in request.
Eg for .../?mykey=myvalue
request.META = {'SERVER_NAME':'127.0.0.1','SERVER_PORT':8000, 'REQUEST_METHOD':'GET', 'QUERY_STRING': 'mykey=myvalue'}
request.GET.__setitem__(key='mykey', value='myvalue')
I struggled with a similar situation and here is the solution I came up with, I started it on an earlier version of Django but it is currently in use on version 2.0.3.
First issue: when you set things to be cached in Django, it sets headers so that downstream caches -- including the browser cache -- cache your page.
To override that, you need to set middleware. I cribbed this from elsewhere on StackOverflow, but can't find it at the moment. In appname/middleware.py:
from django.utils.cache import add_never_cache_headers
class Disable(object):
def __init__(self, get_response):
self.get_response = get_response
def __call__(self, request):
response = self.get_response(request)
add_never_cache_headers(response)
return response
Then in settings.py, to MIDDLEWARE, add:
'appname.middleware.downstream_caching.Disable',
Keep in mind that this approach completely disables downstream caching, which may not be what you want.
Finally, I added to my views.py:
def expire_page(request, path=None, query_string=None, method='GET'):
"""
:param request: "real" request, or at least one providing the same scheme, host, and port as what you want to expire
:param path: The path you want to expire, if not the path on the request
:param query_string: The query string you want to expire, as opposed to the path on the request
:param method: the HTTP method for the page, if not GET
:return: None
"""
if query_string is not None:
request.META['QUERY_STRING'] = query_string
if path is not None:
request.path = path
request.method = method
# get_raw_uri and method show, as of this writing, everything used in the cache key
# print('req uri: {} method: {}'.format(request.get_raw_uri(), request.method))
key = get_cache_key(request)
if key in cache:
cache.delete(key)
I didn't like having to pass in a request object, but as of this writing, it provides the scheme/protocol, host, and port for the request, pretty much any request object for your site/app will do, as long as you pass in the path and query string.
One more updated version of Duncan's answer: had to figure out correct meta fields: (tested on Django 1.9.8)
def invalidate_cache(path=''):
import socket
from django.core.cache import cache
from django.http import HttpRequest
from django.utils.cache import get_cache_key
request = HttpRequest()
domain = 'www.yourdomain.com'
request.META = {'SERVER_NAME': socket.gethostname(), 'SERVER_PORT':8000, "HTTP_HOST": domain, 'HTTP_ACCEPT_ENCODING': 'gzip, deflate, br'}
request.LANGUAGE_CODE = 'en-us'
request.path = path
try:
cache_key = get_cache_key(request)
if cache_key :
if cache.has_key(cache_key):
cache.delete(cache_key)
return (True, 'successfully invalidated')
else:
return (False, 'cache_key does not exist in cache')
else:
raise ValueError('failed to create cache_key')
except (ValueError, Exception) as e:
return (False, e)
The solution is simple, and do not require any additional work.
Example
#cache_page(60 * 10)
def our_team(request, sorting=None):
...
This will set the response to the cache with the default key.
Expire a view cache
from django.utils.cache import get_cache_key
from django.core.cache import cache
def our_team(request, sorting=None):
# This will remove the cache value and set it to None
cache.set(get_cache_key(request), None)
Simple, Clean, Fast.
I have the following code
def ajax_login_request(request):
try:
request.POST[u'login']
dictionary = request.POST
except:
dictionary = request.GET
user = authenticate(username = dictionary[u'login'], password = dictionary[u'password'])
if user and user.is_active:
login(request, user)
result = True
else:
result = False
response = HttpResponse(json.dumps(result), mimetype = u'application/json')
return response
which is being called via ajax. I'm a noob and this is from an example in a book. Unfortunately the version of Django I'm using throws a CSRF error on this. I've done the other CSRF bits, but I don't know how to change the HttpResponse bit to a render call. I do not want to use CSRF_exempt, because I have no idea when that is appropriate. Can someone please provide me the equivalent render call for the HttpResponse above.
Thanks
To make your original code work, you need to get a RequestContext object and pass it along with your response, something like this:
from django.http import HttpResponse
from django.template import RequestContext, Template
def ajax_login_request(request):
# ...
# This bit of code adds the CSRF bits to your request.
c = RequestContext(request,{'result':json.dumps(result)})
t = Template("{{result}}") # A dummy template
response = HttpResponse(t.render(c), mimetype = u'application/json')
return response
Do read up on the CSRF documentation as you might run into strange errors if you don't understand all the ways CSRF is "wired" in your app. The page also has a javascript snippet to make sure CSRF cookies are sent with your ajax requests if you are sending them without a form.
You can also use the render_to_response() shortcut, but you would need to have an actual template to load (in your case, you don't need a template, hence the "dummy" template in my example).
Ok, I'm going to re-draft this answer so you understand where I'm coming from. The CSRF middleware works like this:
You make request -------> request hits csrf --(invalid/no token)--> render 403
middleware
|
(valid token)
|
\ /
Call view
|
\ /
middleware sets
csrf cookie
|
\ /
Response appears
In other words, if you are seeing a 403 csrf page, your view was never called. You can confirm this by sticking a spurious print statement in the view and watching the output from runserver when you make your request.
To solve this, you either need to disable csrf (not good) or use one of the ajax methods available to you. If the required token is passed in your view will actually be executed.
The reason your view is not called is to prevent the action from the forged site from actually ever taking place - for example, if you denied the template at response time the user would already be logged in. The same behaviour occurs with the function decorators.
As for the middleware setting the cookie, that does not alter or depend on the render function at all - this sets the HTTP header Cookie: ... in the response. All responses in Django are HttpResponse objects until it finally converts them to output; render functions are helpers, but that's not what's causing your problem here.
Edit I'll convert what you've got to a render call. You could do this:
return render_to_response(`ajax_templates/login_response.html`,
{'loginresponse': json.dumps(result)})
Where ajax_templates/login_response.html is just:
{% loginresponse %}
That's it. HttpResponse has a main default argument which is the string to return (literally, the html of the web page); that's what you're doing initially. render_to_response and render are shortcuts to this which do this:
render_to_response called ----> open template asked for --> substitute arguments
|
\ /
django instructs web server <--- return this from view <-- create HttpResponse
to send to client object