Rails - May 2008 - expire_fragment silently does nothing unless you use cache_sweeper?

I''ve run into a very strange problem and I can''t find any docs
or any
code in rails core that can explain it.

The behavior is I have a sweeper which is a pure model sweeper so I
tried to use the

config.active_record.observers = [:my_sweeper]

to make it work. However it looks like if I don''t use the
cache_sweeper declaration in the controller, the sweeper gets invoked
but the call to expire_fragment simply does nothing. I found only one
very slight reference to this in a post online -
http://www.ruby-forum.com/topic/145163#643061. But this seems to be a
highly obscure problem. Any ideas?

I put a ''puts'' call into the rails core expire_cache method
and it
appears to never get there..so the logical explanation is that someone
has overridden expire_cache somewhere to make it silently do nothing
and I can''t seem to find where.

The whole point here is that I want my sweepers to act completely
transparently. I don''t want to declare them in every controller. They
should just observe models and act on them. But this behavior is
getting in the way.

thanks!
Yan Pritzker
skwpspace.com
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On 5/11/08, skwp <yan.pritzker-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
>  I''ve run into a very strange problem and I can''t find
any docs or any
>  code in rails core that can explain it.
>
>  The behavior is I have a sweeper which is a pure model sweeper so I
>  tried to use the
>
>  config.active_record.observers = [:my_sweeper]
>
>  to make it work. However it looks like if I don''t use the
>  cache_sweeper declaration in the controller, the sweeper gets invoked
>  but the call to expire_fragment simply does nothing. I found only one
>  very slight reference to this in a post online -
>  http://www.ruby-forum.com/topic/145163#643061. But this seems to be a
>  highly obscure problem. Any ideas?
>
>  I put a ''puts'' call into the rails core expire_cache
method and it
>  appears to never get there..so the logical explanation is that someone
>  has overridden expire_cache somewhere to make it silently do nothing
>  and I can''t seem to find where.
>
>  The whole point here is that I want my sweepers to act completely
>  transparently. I don''t want to declare them in every controller.
They
>  should just observe models and act on them. But this behavior is
>  getting in the way.
CacheSweepers need a controller instance to know how to expire caches.
 That''s why the controller filters used by the #cache_sweeper method
in controllers are needed.

I see four solutions:

* Use #cache_sweeper in every controller that model is modified

* Add this bit of code to make sure your cache sweepers don''t bomb
when they fire outside of controller filters:

class MySweeper
  def after_save(record)
    return if controller.nil?
    expire_cache /blah/
  end
end

* Set some #controller to some mock controller object that knows
enough about routing and ActionController::Caching to expire the cache
properly.  Though this could cause some confusion if people are
expecting other controller methods to be available too.

* Use some unique value that changes every time the record is updated
as part of the cache key.
http://blog.leetsoft.com/2007/5/22/the-secret-to-memcached  Only
useful for memcache probably.

-- 
Rick Olson
http://lighthouseapp.com
http://weblog.techno-weenie.net
http://mephistoblog.com

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