Developing Rails plugin: need some metaprog. help

ruby-talk
1

Hi all

I'm developing an authorization plugin that looks like the following so
far:

module Incense
  module Authorization
    def self.included(base_class)
      base_class.extend(ClassMethods)
    end

    module ClassMethods
      def performs_authorization(options = {})
        before_filter :prepare_user

        include(InstanceMethods)
      end
    end
  end

  module InstanceMethods
    private
    def prepare_user
      session[:user] ||= Member.find_by_id(2) # When there's no user_id
in the session, then use #2 for Guest
    ...
  end

Because I extracted this functionality from an application, in
prepare_user() there's still a hardwired "Member" model used. But in
another application I need this to be a "User" model, so I'd like to be
able to specify the model to use in the options hash of the
performs_authorization() method. So how can I achieve this? Do I have to
use define_method() in the context of performs_authorization? This would
work, I guess, but I don't like it very much... Isn't there another way?

Thanks
Josh

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2

Maybe I can pass arguments to include() somehow?

include(InstanceMethods, model_to_use)

?

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3

Hi Joshua,

I'm developing an authorization plugin that looks like the
following so far:

module Incense
  module Authorization
    def self.included(base_class)
      base_class.extend(ClassMethods)
    end

    module ClassMethods
      def performs_authorization(options = {})
        before_filter :prepare_user

        include(InstanceMethods)
      end
    end
  end

  module InstanceMethods
    private
    def prepare_user
      session[:user] ||= Member.find_by_id(2) # When there's no user_id
in the session, then use #2 for Guest
    ...
  end

Because I extracted this functionality from an application, in
prepare_user() there's still a hardwired "Member" model used.
But in another application I need this to be a "User" model, so
I'd like to be able to specify the model to use in the options
hash of the performs_authorization() method. So how can I
achieve this? Do I have to use define_method() in the context of
performs_authorization? This would work, I guess, but I don't like
it very much... Isn't there another way?

A simple way consists in storing the options hash as a class
variable, you can then create instance and class method
to get the class from the options hash :

def performs_authorization(options = {})
   before_filter :prepare_user

   cattr_accessor :options
   self.options = options

   include(InstanceMethods)
end

# give the name you want
def user_model
   options[:user_model]
end

module InstanceMethods
  private
  def user_model
     self.class.user_model
  end

  def prepare_user
    session[:user] ||= user_model.find_by_id(2)
     ...
  end
end

HTH,

   -- Jean-François.

4

Maybe I can pass arguments to include() somehow?

include(InstanceMethods, model_to_use)

That should be fine. Until you try to access it, it's just a variable.
You can have

variable.do_something()

and then later assign different objects to that variable. e.g.:

def sound(beast)
  beast.make_noise
end

and then

sound(Cow) # => "moo"
sound(Dog) # => "woof"
sound(Rabbit) # => "squee"

···

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Giles Bowkett

Podcast: http://hollywoodgrit.blogspot.com
Blog: http://gilesbowkett.blogspot.com
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Tumblelog: http://giles.tumblr.com

5

Thank you, Jean-François! But is this good style? I'm always looking for
well written patterns, and maybe I should dig deeper into Rails for
having a better overwiew about how they do things. :slight_smile:

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