ActiveRecord#as_param

as_param.rb

module AsParam
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def as_param(param, methods={})
      define_method :to_param do
        value = send(param)
        methods[:out] ? value.send(methods[:out]) : value
      end
      define_singleton_method :find do |*args|
        value = args.shift
        value = value.send(methods[:in]) if methods[:in]
        self.send("find_by_#{param}", value, *args)
      end
    end
  end
end

ActiveRecord::Base.send :include, AsParam

person.rb

class Person < ActiveRecord::Base
  as_param :name, { :in => :upcase, :out => :downcase } # methods called as value comes out / queries datastore
end

rails console

>> Person.all
=> [#<Person id: 1, name: "John">]
>> Person.first.to_param
=> "john"
>> Person.find("john")
=> #<Person id: 1, name: "John>

# essentially,
# with as_param.rb in config/initializers
# and with "resources :people" in config/routes
# we get: /person/:name routes
# and find(params[:id]) uses find_by_name