Agile Web Development with Rails, Edition 5

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/20171113144102_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

      create      test/system/line_items_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

      create      app/views/line_items/_line_item.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 20171113144102_create_line_items.rb 20171113000003_create_line_items.rb

== 20171113000003 CreateLineItems: migrating ==================================

-- create_table(:line_items)

   -> 0.0016s

== 20171113000003 CreateLineItems: migrated (0.0016s) =========================

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_url

end

  test "should destroy product" do

    assert_difference('Product.count', -1) do

      delete product_url(@product)

end

    assert_redirected_to products_url

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 60691

# Running:

.......................

Finished in 0.437990s, 52.5126 runs/s, 77.6273 assertions/s.

23 runs, 34 assertions, 0 failures, 0 errors, 0 skips