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From Leszek Gawron <>
Subject Re: JXTG and caching
Date Tue, 01 Jun 2004 09:41:19 GMT
Sylvain Wallez wrote:

> Leszek Gawron wrote:
>> Sylvain Wallez wrote:
>>>  <page jx:cache-key="" 
>>> jx:cache-validity="">
>> One question: if this NewsHelper is NOT an avalon component (or object 
>> instantiated by flow.createObject) then it doesn't have acces to any 
>> backend logic or data (for example database that stores expiration 
>> time for different news services). Would it be possible to instantiate 
>> this object via flow.createObject analogy?
> Two anwsers to this:
> - we could add a builtin "createObject()" to the JXG expression 
> language, thus directly solving your problem. I don't think this is a 
> good idea as it opens the door to too much code in the template.
I do not like it either.

> - the NewsHelper object can be created in the flow and passed as 
> viewData. This keeps things clean: the flow gives necessary data to the 
> view, and the view pulls what it needs from that data, including means 
> to compute the cache information.
That's fine by me. It's nearly the same what I proposed (if not the same). If 
somebody gave me some points I would like to implement some version of it.

Thinking out loud:
1. flow passes cache info to template via some object instance that provides 
cache key and validity. It could be 2 objects (one for key one for validity) 
but it looks like one object is cleaner (we could impose some interface - is 
there one in cocoon already?)

2. There is CachingJXTemplateGenerator that extends the one we have now.

3. CJXTG implements getKey() and getValidity(). According to cocoon docs if 
null is passed from these methods the result is not being cached. So we could 
even modify the existing generator and have only one that does caching or not.

4. "Compiled" page template has to hold 2 more values - cache key and validity 
assuming the values are Jexl or JXpath expressions.

5. getValidity() and getKey() have access to the template and flow bizData 
(via FlowHelper). When invoked they get appropriate jexl(jxpath) expression 
and evaluate it against bizData. If there is no jx:cache-key jx:validity 
defined then null is returned and no caching is being performed.

6. voilla we have a jxtemplate that is very performant for sites slashdot like 
  (I mean lots of reads, infrequent page updates).

I would like to become an active contributor but the entry step is too big 
without your help. I know it sounds a bit like a waste of time talking some 
simple functionality over and then doing the review instead of implementing it 
by oneself but if you choose the first variant you'll have a new active 
contributor in some future (near I hope).

Leszek Gawron

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