Rails - May 2007 - cache everything but...

I saw this older post when searching for information:

On Feb 16, 5:10 pm, Ingo Weiss
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> withfragmentcachingonecancacheparts of a page. However, more often
> than not what I would need is the exact opposite approach. I would like
> to be able to use action cashing and have a mechanism for telling Rails
> to excludeoneor more areas from the cashing and fill them with dynamic
> content instead. A good example would be a page whereallcontent would
> be perfectly cachablebutonetiny line saying ''logged in as
> [username]''.
>
> Wouldn''t a mechanism for doing this more elegantly be a great
addition
> to Rails? Or am I missing something and this is in fact currently
> possible?
I have exactly the same need - a front page that has a bit of text
that changes depending on whether the user is logged in or not.
Everything else could be cached using page cacheing.

Hrm.... I''ll take a look at the code... maybe something like
''cache_except'' is possible?

Thanks,
Dave
--
http://www.dedasys.com/davidw/


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davidnwelton-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
wrote:
> I saw this older post when searching for information:
>
> On Feb 16, 5:10 pm, Ingo Weiss
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
> wrote:
>
>   
>> withfragmentcachingonecancacheparts of a page. However, more often
>> than not what I would need is the exact opposite approach. I would like
>> to be able to use action cashing and have a mechanism for telling Rails
>> to excludeoneor more areas from the cashing and fill them with dynamic
>> content instead. A good example would be a page whereallcontent would
>> be perfectly cachablebutonetiny line saying ''logged in as
>> [username]''.
>>
>> Wouldn''t a mechanism for doing this more elegantly be a great
addition
>> to Rails? Or am I missing something and this is in fact currently
>> possible?
>>     
>
> I have exactly the same need - a front page that has a bit of text
> that changes depending on whether the user is logged in or not.
> Everything else could be cached using page cacheing.
>
> Hrm.... I''ll take a look at the code... maybe something like
> ''cache_except'' is possible?
>
> Thanks,
> Dave
> --
> http://www.dedasys.com/davidw/
>   
Hey

I had the same issue and settled for two cashed versions of my page, one
for logged in users and one for visitors.
I put the code changes into a plugin you might want to have a look at.

http://rails.co.za/articles/2007/01/10/cachefilter-update
and then some bug fixes later...
http://rails.co.za/articles/2007/02/07/cachefilter-rails-1-2-and-edge-compatible

HTH

Gustav Paul

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> > I have exactly the same need - a front page that has a bit of text
> > that changes depending on whether the user is logged in or not.
> > Everything else could be cached using page cacheing.
> I had the same issue and settled for two cashed versions of my page, one
> for logged in users and one for visitors.
> I put the code changes into a plugin you might want to have a look at.
>
> http://rails.co.za/articles/2007/01/10/cachefilter-update
> and then some bug fixes
later...http://rails.co.za/articles/2007/02/07/cachefilter-rails-1-2-and-edge...
Looks like a good way of doing it.

I was thinking about something like this:

1) Create a no_cache method as a helper.  The trick is that it outputs
something like <%= blah blah %>
2) Cache the page.
3) Render the cached version, which does the substitution on what
no_cache slipped into the cache.

I don''t know whether how efficient that is, since the whole page still
has to be parsed up for erb, when there is only one little chunk of
it.  I also don''t know if there are any lurking problems...

Thanks,
Dave
--
http://www.dedasys.com/davidw/


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> I was thinking about something like this:
>
> 1) Create a no_cache method as a helper.  The trick is that it outputs
> something like <%= blah blah %>
> 2) Cache the page.
> 3) Render the cached version, which does the substitution on what
> no_cache slipped into the cache.
Ok, some code that seems to work:

class NoCacheFilter

  include ActionController::Caching::Actions

  def initialize(*actions, &block)
    @actions = actions
  end

  def before(controller)
    return unless @actions.include?(controller.action_name.intern)
    controller.instance_variable_set ''@dont_interpolate_this'',
true
    action_cache_path = ActionCachePath.new(controller)
    if cache = controller.read_fragment(action_cache_path.path)
      controller.rendered_action_cache = true
      set_content_type!(action_cache_path)
      controller.send(:render, :inline => cache)
      false
    end

  end

  def after(controller)
    return if !@actions.include?(controller.action_name.intern) ||
controller.rendered_action_cache
    controller.write_fragment(ActionCachePath.path_for(controller),
controller.response.body)
    controller.send(:render, :inline => controller.response.body)
  end

  private
  def set_content_type!(action_cache_path)
    if extention = action_cache_path.extension
      content_type = Mime::EXTENSION_LOOKUP[extention]
      action_cache_path.controller.response.content_type content_type.to_s
    end
  end

end

Combined with this helper:

  def no_cache(text)
    return eval(text) unless @dont_interpolate_this
    return "<%= #{text} %>"
  end

Things that could perhaps be improved:

1) I don''t like setting the variable in the controller.
2) I don''t really like the fact that no_cache takes text as an
argument rather than somehow accomplishing the same thing with a
block, but there''s no way to get a block''s text out, so a
string it
is, as far as I can tell.


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>   def after(controller)
>     return if !...@actions.include?(controller.action_name.intern) ||
> controller.rendered_action_cache
>     controller.write_fragment(ActionCachePath.path_for(controller),
> controller.response.body)
>     controller.send(:render, :inline => controller.response.body)
>   end
Ugh, that isn''t quite right, either, because apparently you
can''t do
any sort of render operation in the after filter, not even
render_to_string.  This is pretty hacky feeling, but if that''s what it
takes...

  def after(controller)
    return if !@actions.include?(controller.action_name.intern) ||
controller.rendered_action_cache
    controller.write_fragment(ActionCachePath.path_for(controller),
controller.response.body)
    controller.instance_variable_set ''@performed_render'',
false
    controller.response.body controller.send(:render_to_string, :inline =>
controller.response.body)
  end

Cleaner ideas welcome!


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