Agile Web Development with Rails, Edition 4

9.2 Iteration D2: Connecting Products to Carts

Create line item which connects products to carts'

Create the model object.

rails generate scaffold LineItem product_id:integer cart_id:integer

      invoke  active_record

      create    db/migrate/20120629163106_create_line_items.rb

      create    app/models/line_item.rb

      invoke    test_unit

      create      test/unit/line_item_test.rb

      create      test/fixtures/line_items.yml

       route  resources :line_items

      invoke  scaffold_controller

      create    app/controllers/line_items_controller.rb

      invoke    erb

      create      app/views/line_items

      create      app/views/line_items/index.html.erb

      create      app/views/line_items/edit.html.erb

      create      app/views/line_items/show.html.erb

      create      app/views/line_items/new.html.erb

      create      app/views/line_items/_form.html.erb

      invoke    test_unit

      create      test/functional/line_items_controller_test.rb

      invoke    helper

      create      app/helpers/line_items_helper.rb

      invoke      test_unit

      create        test/unit/helpers/line_items_helper_test.rb

      invoke  stylesheets

   identical    public/stylesheets/scaffold.css

rake db:migrate

mv 20120629163106_create_line_items.rb 20110711000003_create_line_items.rb

==  CreateLineItems: migrating ================================================

-- create_table(:line_items)

   -> 0.0019s

==  CreateLineItems: migrated (0.0020s) =======================================

Cart has many line items.

edit app/models/cart.rb

class Cart < ActiveRecord::Base

  has_many :line_items, :dependent => :destroy

end

Product has many line items.

edit app/models/product.rb

class Product < ActiveRecord::Base

  has_many :line_items

  before_destroy :ensure_not_referenced_by_any_line_item

  #...

  private

    # ensure that there are no line items referencing this product

    def ensure_not_referenced_by_any_line_item

      if line_items.empty?

        return true

      else

        errors.add(:base, 'Line Items present')

        return false

end

end

end

Line item belongs to both Cart and Product (But slightly more to the Cart). Also provide convenient access to the total price of the line item

edit app/models/line_item.rb

class LineItem < ActiveRecord::Base

  belongs_to :product

  belongs_to :cart

end