Rails 4 URL setup to find model instances (eg products) by numerical id for puposes of cart addition and find by slug for purposes of SEO display. Will display in browser as app/products/my-url-goes-here, but will send params as "product_id" => 1. Completely Bonzer!

SEO urls for shopping cart in rails

# PRODUCT MODEL

before_create do
   self.slug = title.downcase.gsub(" ", "-")  
  end

	def to_param
		[id, title.parameterize].join("-")
	end
	
#DB MIGRATION
	
	class AddSlugToProducts < ActiveRecord::Migration
  def change
    add_column :products, :slug, :string
  end
end

#LINEITEMS CONTROLLER

def create
    product = Product.find(params[:product_id])
    @line_item = @cart.add_product(product.id)

#PRODUCT CONTROLLER

private  
    def set_product
      @product = Product.find_by_slug(params[:id])
    end
end
    
#PRODUCT LINKS IN A VIEW

    <%= link_to image_tag(product.image_url, class: "img-responsive", style: "margin-top:10px;
								width:100%;"), product %>
    
    <%= button_to 'Add To Cart', line_items_path(product_id: product), class: "button_example center-block", style: "width:100%;
							  margin:10px 0;" %>