cache_page decorator (memcached) fails with Django 1.3b1 (can't pickle Input object)

[vkojouharov@…]

Hello,

I'm consistently getting an error with each request after upgrading from Django 1.3a1 to 1.3b1.
The settings aren't changed after the upgrade, and if I remove the cache_page decorator, everything is back on track. The url in question is pasted below:

url(r'^/?$', cache_page(views.IndexView.as_view(), timeout), name='main_index')

[vkojouharov@…]

traceback, META and settings

[Russell Keith-Magee]

We're going to need a bit more than a stack trace. We have an test suite checking cache_page, and those tests are passing. There is clearly something special about your page.

We need a reproducible test case to be able to accept this bug. Please reopen if you can provide a simple view that fails in the way you describe.

[urandom]

a simple project which causes the error

[urandom]

I've attached a generic django project, with an app that only contains 1 view that is cached. The only setting that was changed was the cache setting. The apache directory contains the wsgi and virtualhost configs for apache.

Running this through apache reproduces this error. Interestingly, running it through the internal server produces a different error, which is still connected to the cache_page:

a class that defines __slots__ without defining __getstate__ cannot be pickled

[Russell Keith-Magee]

Ah. This is a bit of a problem. The introduction of TemplateResponse means that the cache page decorator can't be used on Template Views. Which is a fairly major omission.

We either need to make generic views use normal responses (and make TemplateResponse an available option), or we need to find a way to let decorators (especially the cache decorator) play nice with TemplateResponse.

This is definitely a 1.3 blocker.

[Russell Keith-Magee]

Test case demonstrating the problem

[Joshua "jag" Ginsberg <jag@…>]

Patch to fix the issue (includes previously attached tests)

[Joshua "jag" Ginsberg <jag@…>]

Attached a patch - it puts pre_render and post_render callbacks into the TemplateResponse and modifies the cache middleware, in the face of a TemplateResponse, to register a callback on the TemplateResponse to store the final rendered copy in cache. I included russelm's test cases in the patch.

-jag

[Russell Keith-Magee]

(In [15295]) Fixed #15012 -- Added post-rendering callbacks to TemplateResponse so that decorators (in particular, the cache decorator) can defer processing until after rendering has occurred. Thanks to Joshua Ginsberg for the draft patch.

[Jacob]

Milestone 1.3 deleted