[Zope-dev] AW: [Summary] Caching prob with AHCM and headers

[Fred Yankowski]

On Fri, Sep 12, 2003 at 10:13:44AM -0400, Tres Seaver wrote:
> The CMF's CachingPolicyManger, which is specialized for caching skin
> methods, already has such customizations:  it allows spelling the
> 'Last-Modified' header using a TALES expression, and also has checkboxes
> for the 'no-cache', 'no-store', and 'must-revalidate' options of the
> 'Cache-Control' header.

Based on that note I decided to try CachingPolicyManager for the first
time, and I'm confused about how it's supposed to work.

In a CMF/Plone portal instance (CMF 1.4) I created a CMF Caching
Policy Manager object.  If I create a policy instance with default
Predicate and Mod. Time values and a Max age of 999, FSImage objects
are then published with appropriate cache control headers so that they
expire after 999 seconds.  Cool.

But I can't see how to create more restrictive Predicate.  My initial
attempt was to set Predicate like so:

	python: content.meta_type == 'Filesystem Image'

But that predicate never seems to return true.  Looking at
_setCacheHeaders() in CMFCore/utils.py, 'content' is set to
'aq_parent(obj)'.  Because of that, any tests against 'content' in the
Predicate apply to the Filesystem Directory View that contains the
particular FSImage objects, rather than to the FSImage object itself.
What good is that?

-- 
Fred Yankowski      fred at ontosys.com           tel: +1.630.879.1312
OntoSys, Inc	    PGP keyID: 7B449345        fax: +1.630.879.1370
www.ontosys.com     38W242 Deerpath Rd, Batavia, IL 60510-9461, USA