gistfile1.rb

# Usage
#    @assets = Asset.my_filter(params[:filter]).public.all # works like a charm
#    @assets = @account.assets.my_filter(params[:filter]).public.paginate({
#      :page  => (params[:page] || 1)
#    }) # works BUT (ofc) does not adhere to the @account scope 
#

# initializer
ActiveRecord::Base.send :include, Spock::Base::Filterable

# some lib file
module Spock
  module Base
    module Filterable
      def self.included(base)
        base.extend ClassMethods
      end
      
      module ClassMethods
        
        def my_filter(f)
          f_name, f_arguments = f.to_s.split(':')
          f_arguments = f_arguments.to_s.split(',')
          if f_name && my_available_filters.include?(f_name.to_sym)
            f_arguments.empty? ? send("filter_#{f_name}".to_sym) : self.scopes["filter_#{f_name}".to_sym].call(self, *f_arguments)
          else
            self
          end
        end
        
        def my_available_filters
          self.scopes.keys.map { |m| m.to_s }.select do |m|
            m =~ /^filter_/
          end.map { |m| m[7..-1].to_sym }
        end
        
      end
      
    end
  end
end



# valid filter scopes in a model
class Asset < ActiveRecord::Base
  named_scope(:filter_placed_in, lambda { |group_id|
    {
      :select => "DISTINCT assets.*",
      :from   => "assets",
      :joins  => "LEFT JOIN placements ON placements.asset_id = assets.id",
      :conditions => "placements.group_id = #{group_id}",
      :order      => "placements.position ASC"
    }
  })
  named_scope(:filter_date, lambda { |date|
    {
      :conditions => ["created_at = ?", date]
    }
  })
  named_scope(:filter_date_range, lambda { |start_date, end_date| { :conditions => ["created_at BETWEEN ? and ?", start_date, end_date] } })
end