class associations apart from models

I want to use several custom classes in the controller. Some of them
are supposed to have certain associations. I know how to work with
associations in the model and I thought that I could do something
similar here.

What I tried is something like this:

module Types

  class System < ActiveRecord::Base
    has_many :resources
    attr_accessor :name
    def initialize(name)
      @name = name
    end
  end

  class Resource < ActiveRecord::Base
    belongs_to :system
    attr_accessor :name
    def initialize(name,system)
      @name = name
      # add to system (?)
    end
  end

end

So how can I specity the System for a Resource or return it?

Thanks,
Max