Rails core - Dec 2005 - call a method once per page request

Hi,

I''m wondering if there is a simple solution to call a method once per
page request.

I tried to place my call in a before_filter in ApplicationController but
it''d called a second time if I use render_component from a view.
Seems to me that a hook should be added in Dispatcher#prepare_application.

Context: working on i18n, I''m trying to check lang either from uri, or
session, or against default lang or browser prefs. This is close to
routing, but I''d prefer not to interfere with routing, would be
simpler.

-- 
Jean-Christophe Michel

* Jean-Christophe Michel (jc.michel@symetrie.com) [051230
17:33]:
> I''m wondering if there is a simple solution to call a method once
per
> page request.
> 
> I tried to place my call in a before_filter in ApplicationController but
> it''d called a second time if I use render_component from a view.
> Seems to me that a hook should be added in Dispatcher#prepare_application.
Seems like a before_filter should be sufficient, simply

def my_method
  return true if @@my_method_called
  @@my_method_called = true
  # do something
end

Perhaps if this is a common idiom, there''s a call for a :once modifier
to before_filter / after_filter (which would do essentially the above)
instead of defining a new hook?

Rick
-- 
 http://www.rickbradley.com    MUPRN: 850
                       |  could forbid lock()ing
   random email haiku  |  readonly packages. Not
                       |  sure which was better.

Rick Bradley a écrit :
>>I''m wondering if there is a simple solution to call a method
once per
>>page request.
>>
> Seems like a before_filter should be sufficient, simply
> 
> def my_method
>   return true if @@my_method_called
>   @@my_method_called = true
>   # do something
> end
Sure it would work. Is it a good practice to use a global for such a
problem ? Seems like a smart hack to me ;-)

-- 
Jean-Christophe Michel

On 2-jan-2006, at 10:48, Jean-Christophe Michel wrote:
>> def my_method
>>   return true if @@my_method_called
>>   @@my_method_called = true
>>   # do something
>> end
>
> Sure it would work. Is it a good practice to use a global for such a
> problem ?
@@class_var.

-- 
Regards, Charles.

Hi all,

My problem is to try to call a method once per page request.
(Context: I want to detect the current lang for localization, and this
has to be done on each request, so lang passed through uri can have
priority over session, browser prefs or default app lang).

The way I followed is to have an independant class, Locale, which method
init is called through an ApplicationController before_filter.
Fine.

But when I use a render_component in my layout, to render a menu for
instance, a second controller is called, and the negociation for the
lang is done once more. To avoid this, I''d like to be sure this method
is called only once (it wastes ressources, and more, I need to be sure
that the lang is consistent through my components on the same page).

Rick Bradley suggested :
> Seems like a before_filter should be sufficient, simply
> 
> def my_method
>   return true if @@my_method_called
>   @@my_method_called = true
>   # do something
> end
Rick, your solution is not working, at least here with scgi+apache2 in
dev mode. The class vars are not reinited on each request, so once
my_method was called, it''s not run any more until the server is
restarted. In my case this mean you cannot change the lang :p
I just tried with webrick and get the same result.


That''s why I concluded that there should be a hook to call some methods
once per page request. Digging in core code, I think it could be around
Dispatcher#prepare_application
in trunk/railties/lib/dispatcher.rb

Opinions ?
-- 
Jean-Christophe Michel

Jean-Christophe Michel wrote:
> Hi all,
>
> My problem is to try to call a method once per page request.
> (Context: I want to detect the current lang for localization, and this
> has to be done on each request, so lang passed through uri can have
> priority over session, browser prefs or default app lang).
>
> The way I followed is to have an independant class, Locale, which method
> init is called through an ApplicationController before_filter.
> Fine.
>
> But when I use a render_component in my layout, to render a menu for
> instance, a second controller is called, and the negociation for the
> lang is done once more. To avoid this, I''d like to be sure this
method
> is called only once (it wastes ressources, and more, I need to be sure
> that the lang is consistent through my components on the same page).
>
> Rick Bradley suggested :
>   
>> Seems like a before_filter should be sufficient, simply
>>
>> def my_method
>>   return true if @@my_method_called
>>   @@my_method_called = true
>>   # do something
>> end
>>     
>
> Rick, your solution is not working, at least here with scgi+apache2 in
> dev mode. The class vars are not reinited on each request, so once
> my_method was called, it''s not run any more until the server is
> restarted. In my case this mean you cannot change the lang :p
> I just tried with webrick and get the same result.
>
>
> That''s why I concluded that there should be a hook to call some
methods
> once per page request. Digging in core code, I think it could be around
> Dispatcher#prepare_application
> in trunk/railties/lib/dispatcher.rb
>
> Opinions ?
>   
I suggest to place language information on the request object. Add an 
attr_accessor to class AbstractRequest

class ActionController::AbstractRequest
  attr_accessor :language
end

and set this in your controller

class ApplicationController < ActionController::Base
  def language
    request.language ||= your_expensive_language_computation
  end
  helper_method :language
end

Another option would be to install a filter that sets language on the 
request object and store it in @language on the controller for direct 
access. From there it will be propagated to your views automatically.

class ApplicationController < ActionController::Base
  before_filter :set_language
  private
    def set_language
       @language = (request.language ||= 
your_expensive_language_computation)
    end
end

and use @language directly (similar to the method described in 
http://railsexpress.de/blog/articles/2005/11/18/components-may-not-be-evil-but-they-sure-can-be-slow)

-- stefan

-- 
For rails performance tuning, see: http://railsexpress.de/blog
Subscription: http://railsexpress.de/blog/xml/rss20/feed.xml

On 12-Jan-06, at 2:56 AM, Stefan Kaes wrote:
> I suggest to place language information on the request object. Add  
> an attr_accessor to class AbstractRequest
>
> class ActionController::AbstractRequest
>  attr_accessor :language
> end
My preference has always been to add an "attributes" method to the  
request.  It saves having to go back and define accessors for every  
''expensive'' item being tracked.

in vendor/plugins/request_attributes/init.rb

ActionController::AbstractRequest.class_eval do
   def attributes
     @request_attributes ||= Hash.new()
   end
end

Regards,
Trevor

--
Trevor Squires
http://somethinglearned.com