related_products_extension.rb

# Uncomment this if you reference any of your controllers in activate
# require_dependency 'application'

class RelatedProductsExtension < Spree::Extension
  version "1.0"
  description "Describe your extension here"
  url "http://yourwebsite.com/relations"

  # Please use relations/config/routes.rb instead for extension routes.

  # def self.require_gems(config)
  #   config.gem "gemname-goes-here", :version => '1.2.3'
  # end

  def activate
    Calculator::RelatedProductDiscount.register

    Product.class_eval do
      has_many :relations, :as => :relatable

      def self.relation_types
        RelationType.find_all_by_applies_to(self.to_s, :order => :name)
      end

      def method_missing(method)
        relation_type =  self.class.relation_types.detect { |rt| rt.name.downcase.gsub(" ", "_").pluralize == method.to_s.downcase }

        if relation_type.nil?
          super(method)
        else
          relations.find_all_by_relation_type_id(relation_type.id).map(&:related_to).select {|product| product.deleted_at.nil? && product.available_on <= Time.now()}
        end

      end
    end

    Admin::ProductsController.class_eval do
      def related
        load_object
        @relation_types = Product.relation_types
      end
    end

  end
end