Disable Jinja template caching for certain filter

user_20247 0
Viewed 2510

We have a custom Jinja filter that we use for creating cache busting URL for our Javascript and CSS resources. We now noticed that in our production environment the final, compiled templates get cached. This results in a problem since our template filter sometimes doesn't create a new URL (i.e. when the template wasn't changed but the Javascript was).

Is there a way to force Jinja to reevaluate a certain filter every time and don't cache the result?

Edit 1: We are using constant inputs (name of the file) to the filter.

jinja2
4 Answers

After lots of Googling, I finally found the real solution to this. Jinja has a special helper called contextfilter that you can use to decorate your function with to make your filter context-aware (and context-dependent). The Jinja bytecode cache will not cache this computed value, even when a constant is passed as input.

In your filter in Python:

from jinja2 import contextfilter

@contextfilter
def asset_url(context, url):
    return some_url_thing(url)

In your template:

<link rel="stylesheet" href="{{ 'styles.css' | asset_url }}" />
user_9696210

The easiest way to do this is:

On your flask server script do this:

from time import ctime

In your app.route() function,

in the return line add: 

time=ctime()

for example:

return render_template('signup', error = error, time = ctime())

In the html reference for your css file(if using jinja2) add:

?{{time}}

at the end of your reference line.

That shoud look like this:

<link rel="stylesheet" href="{{ url_for('static', filename='css/base.css')}}?{{time}}">

Worked pretty good for me and the browser stopped caching.

I hope it helps!

Cheers!

-Nelio

user_122345940
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