Agile Web Development with Rails, Edition 4

Agile Web Development with Rails, Edition 4

9.3 Iteration D3: Adding a button 9.1 Iteration D1: Finding a Cart

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/20111029071357_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  assets
      invoke    coffee
      create      app/assets/javascripts/line_items.js.coffee
      invoke    scss
      create      app/assets/stylesheets/line_items.css.scss
      invoke  scss
   identical    app/assets/stylesheets/scaffolds.css.scss
rake db:migrate
mv 20111029071357_create_line_items.rb 20110711000003_create_line_items.rb
==  CreateLineItems: migrating ================================================
-- create_table(:line_items)
   -> 0.0549s
==  CreateLineItems: migrated (0.0549s) =======================================
 

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

9.3 Iteration D3: Adding a button 9.1 Iteration D1: Finding a Cart