Agile Web Development with Rails, Edition 5

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:references cart:belongs_to
      invoke  active_record
      create    db/migrate/20160507014147_create_line_items.rb
      create    app/models/line_item.rb
      invoke    test_unit
      create      test/models/line_item_test.rb
      create      test/fixtures/line_items.yml
      invoke  resource_route
       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/controllers/line_items_controller_test.rb
      invoke    helper
      create      app/helpers/line_items_helper.rb
      invoke      test_unit
      invoke    jbuilder
      create      app/views/line_items/index.json.jbuilder
      create      app/views/line_items/show.json.jbuilder
      invoke  assets
      invoke    coffee
      create      app/assets/javascripts/line_items.coffee
      invoke    scss
      create      app/assets/stylesheets/line_items.scss
      invoke  scss
   identical    app/assets/stylesheets/scaffolds.scss
rails db:migrate
mv 20160507014147_create_line_items.rb 20160506000003_create_line_items.rb
== 20160506000003 CreateLineItems: migrating ==================================
-- create_table(:line_items)
   -> 0.0071s
== 20160506000003 CreateLineItems: migrated (0.0072s) =========================
 

Cart has many line items.

edit app/models/cart.rb
class Cart < ApplicationRecord
  has_many :line_items, dependent: :destroy
end

Product has many line items.

edit app/models/product.rb
class Product < ApplicationRecord
  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
      unless line_items.empty?
        errors.add(:base, 'Line Items present')
        throw :abort
      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 < ApplicationRecord
  belongs_to :product
  belongs_to :cart
end

Add a test ensuring that non-empty carts can't be deleted.

edit test/controllers/products_controller_test.rb
  test "can't delete product in cart" do
    assert_difference('Product.count', 0) do
      delete product_url(products(:two))
    end
 
    assert_redirected_to products_path
  end
 
  test "should destroy product" do
    assert_difference('Product.count', -1) do
      delete product_url(@product)
    end
 
    assert_redirected_to products_path
  end

change fixture so that product two is in both carts

edit test/fixtures/line_items.yml
# Read about fixtures at http://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
 
one:
  product: two
  cart: one
 
two:
  product: two
  cart: two
rails test:controllers
Run options: --seed 15401
 
# Running:
 
.......................
 
Finished in 0.562729s, 40.8722 runs/s, 78.1903 assertions/s.
 
23 runs, 44 assertions, 0 failures, 0 errors, 0 skips

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