Rails - Feb 2007 - How to make a per-request variable globally available?

I''m developing a single application that responds to requests from two
domains. Various parts of my code need to work differently depending on
the request''s domain.

The typical solution would be to do something like this:

class ApplicationController < ActionController::Base
  before_filter :initialize_site

  # makes @site available to all controllers and views
  def initialize_site
    @site = Site.find_by_domain(request.domain)
  end
end

class Site < ActiveRecord::Base
  def find_by_domain(domain)
    # ...
  end
end


The problem is that I''d really like to have access to @site in my
models
as well, because it would make my controllers much much more DRY.

In this (contrived) example, imagine two seperate store-fronts, both
selling widgets from the same manufacturer. But we want some widgets to
appear in one store, and some in the other.

class Widget < ActiveRecord::Base
  belongs_to :manufacturer
  belongs_to :site
end

class Site < ActiveRecord::Base
  has_many :widgets
end

class Manufacturer < ActiveRecord::Base
  # This is bad because Manufacturer.find(1).widgets contains
  # widgets from both sites
  has_many :widgets

  # I want to do the following instead, but I can''t because
  # @site is not available to models because it''s a controller
  # instance variable:
  has_many :widgets, :conditions => {:site_id => @site.id}
end



So I have to do things like this instead:

class ManufacturersController < ApplicationController
  def show
    @manufacturer = Manufacturer.find(params[:id])

    @widgets = @manufacturer.widgets.select do |widget|
      widget.site == @site
    end
  end
end

Having to do things like that in almost every action in my controllers
is driving me nuts. It''s horribly un-DRY. I want to take care of the
site filtering at the model level, so my controllers and views don''t
even know the difference.

So the question is, what''s the best-practice for making a variable
available to all models, views, and controllers? A (gasp!) global
variable? This variable needs to be set at the beginning of each
request.

Completely different approaches to solving this problem much appreciated
as well.

Thanks for reading!

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>   # makes @site available to all controllers and views
>   def initialize_site
>     @site = Site.find_by_domain(request.domain)
>   end
> end
>
You can use Thread.current to pass data to your models.  Something
like this:

def initialize_site
  @site = Site.find_by_domain(request.domain)
  Thread.current[:site] = @site
end

Aaron


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I have been playing with the id of something similar and have come up 
with this.

make a folder domains then for each domain add public, config and any 
other files you need to be site specific.

then start 2 seperate fcgi proccesses

if you set it up properly you can run two domains off the same 
application; and can put SITE in the enviroments folder

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Aaron wrote:
> You can use Thread.current to pass data to your models.  Something
> like this:
> 
> def initialize_site
>   @site = Site.find_by_domain(request.domain)
>   Thread.current[:site] = @site
> end
Thank you, that''s exactly what I needed.

After I did that I extended ActiveRecord.Base::find to put my conditions 
in at the highest level:

class Site < ActiveRecord::Base
  def Site.current
    Thread.current[:site]
  end
end

class Widget < ActiveRecord::Base
  class << self
    # keep a pointer to the old find
    alias :find_without_site :find

    # extend find to always return widgets for the current site
    def find(*args)
      self.with_scope(:find => {:conditions => {:site_id => 
Site.current.id}}) do
        self.find_without_site(*args)
      end
    end
  end
end


And it''s amazing. All unnecessary references to the site are gone from 
my controllers, and even the other models. Thanks again!

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> Thank you, that''s exactly what I needed.
Your welcome
> class Widget < ActiveRecord::Base
>   class << self
>     # keep a pointer to the old find
>     alias :find_without_site :find
>
>     # extend find to always return widgets for the current site
>     def find(*args)
>       self.with_scope(:find => {:conditions => {:site_id =>
> Site.current.id}}) do
>         self.find_without_site(*args)
>       end
>     end
>   end
> end
>
> And it''s amazing. All unnecessary references to the site are gone
from
> my controllers, and even the other models. Thanks again!
Scoped finds are great, and overriding the default find will
automatically scope your associations too.  But be aware that the
find_by convenience methods (find_by_name, find_by_id, etc...) are NOT
scoped.

Aaron


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