cache everything but...

I saw this older post when searching for information:

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

davidnwelton@gmail.com wrote:

I saw this older post when searching for information:

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

> 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

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.

  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!