Problems with Django template cache refresh_问答_开发者

I was trying to write a simple app in Django to cache some external images and display / refresh them on request.

What I do is:

{% load cache %} {% cache 1500 image %} {% endcache %}

and refresh does this in a view code when refresh "button" is clicked on:

key = "template.cache.image.d41d8cd98f00b204e9800998ecf8427e" cache.delete( key )

Now it works all fine when an image gets removed or I replace the src with some different value. It also works when I type something inside {% cache ... %} {% endcache %}tags, but when an image changes - like I replace it by some other one - the refresh button makes nothing with it until I refresh the whole page with browser's refresh button (or by using F5). I tested it on Chrome (some version) and Opera (11). My view does n开发者_StackOverflowot use any cache options, but I tried it with @never_cache and some other tags and nothing helped.

I hope you can help me out with it.

Best regards.

Edit: What I exactly try to do is to cache an image and refresh it on request. Maybe it requires some python work to get an image, cache response hash and then re-cache the image (by removing it if its previous hash changes), but I have no idea how to 'send' image through python HttpResponse / render_to_response to "html form" to display it.

Ken's answer works for me.

If you are using django, in the template, just use something like

    <img src="/image.jpg?cachebuster={{uuid}}" />

and pass the uuid from server side.

I'd like to vote up Ken's answer but unfortunately I don't have enough reputation to do so. Sorry I have to answer this question again.

Are you keeping the same image name but changing the image? I'm guessing it is the browser cache that is causing you problems and not the django cache.

Try adding a query string to the end of the image, it should help invalidate the browser cache. it doesn't matter what you put in they query string, it just needs to be unique

<img src="/image.jpg?cachebuster=blah23" />

I was having a browser cache refresh problem, and Ken Cochrane's answer led me to a solution.

My problem was with the model detail page. After updating the record, coming back to the detail page, the browser showed what was in the cashe -- the page without the updates. This sucked big time! Imagine a user's confusion after saving some updates, only to misunderstand from the (browser cache version of) detail page that the updates were not saved! But they were saved, the problem was the browser was showing the cached version.

Ken Cochrane's solution: adding a query string with something unique. That worked for me! At first, I just added timezone.now() formatted to be URL compatible, such as ?utc=2018-02-19_22.57.30 (in URLs, colons proceed the port, colons confuse the URL -- cannot use colons).

The python format string: '%Y-%m-%d_%H.%M.%S'

This solved my problem, but this was forcing a refresh every time the user came back to the detail view page, even when there had been no update. Then it occurred to me: instead of using timezone.now(), use the model row's last update timestamp. After an update, the last update timestamp will be later than the prior one, so the browser will refresh. If the user comes back again without any update, the the last update timestamp will be the same, so the browser can show the cached page.

So my query string is ?updated=2018-02-19_22.57.30

The solution could be used when keeping the same image name but changing the image file by using the file system timestamp of the image file for the query string. Only when the image changes, the timestamp will be different, and the browser will refresh. When the image file is the same, the timestamp will be the same, so the browser can show the cached version.