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/20100606143405_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 20100606143405_create_line_items.rb 20100301000003_create_line_items.rb

(in /home/rubys/svn/rails4/Book/util/work-193/depot)

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

-- create_table(:line_items)

   -> 0.0019s

==  CreateLineItems: migrated (0.0019s) =======================================

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

  # ensure that there are no line items referencing this product

  def ensure_not_referenced_by_any_line_item

    if line_items.count.zero?

      return true

    else

      errors[:base] << "Line Items present"

      return false

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