Cart Creation

What we’ll cover

• Using Sessions• Public, Private, and Protected Methods in

Ruby• Relationships between models• Active Record Callbacks & Validation• Adding a button to a page• More Functional Testing

Generate a shopping cart

• rails generate scaffold cart– No foreign keys present– Only one of the tables has a foreign key

• Need to recover the cart with every request

Rails Sessions

• By default, session info stored in a browser session cookie (4k limit)– Database or memcached also available

• Don’t store data that can easily be outdated– Serialized ActiveRecord objects

• Cryptographically signed but unencrypted• Don’t store critical information solely in the

session

Associate the cart with a session

• app/controllers/application_controller.rb

private def current_cart

Cart.find(session[:cart_id]) rescue ActiveRecord::RecordNotFound cart = Cart.create session[:cart_id] = cart.id cart

end

Public, Private, & Protected Methods

• Different from Java & C#• Public methods can be invoked by anyone • Private methods accessible by an object from a

derived class• Protected methods accessible by other objects

& objects from derived classes• Inheritance doesn’t determine method visibility– Private & protected methods visible from

subclasses

Storing items in the cart

• rails generate scaffold line_item product_id:integer cart_id:integer– By convention, singular of table name appended

with “_id”– Need to establish relationship in both the

database and the model– Model declarations add ability to build and

navigate the relationship

ActiveRecord relationships

• One to One– has_one :contained– belongs_to :container

• One to Many– has_many :contained– belongs_to :container

• Table with foreign keys has the ‘belongs_to’

Add Relationship Specifiers

class Cart < ActiveRecord::Base has_many :line_items, :dependent => :destroyend

class LineItem < ActiveRecord::Base belongs_to :product belongs_to :cartend

class Product < ActiveRecord::Base has_many :line_itemsend

What if we destroy a cart?

• Line_items dependent on cart– :dependent => :destroy indicates that line_items

are destroyed along with the cart– destroy involves ActiveRecord validation logic,

delete only removes from the database

What if we destroy a product?

• Make sure it isn’t contained in a cart

ActiveRecord Callbacks & Validations

• Callbacks invoked before & after operations– For example save, delete, create, validate– Can view unformatted data in ‘before’ callbacks• Dates & Currency

• Returning the actual value ‘false’ stops the operation

• Add a handler or define as a method

Add a button• Won’t be creating a new controller or a new action

– Creating an item in the cart, so use line_item controller– Looking at generated code in line_item_controller.rb, we’ll use

the ‘Create’ action– ‘Create’ action called using HTTP Post

• button_to ‘button label’, ‘URL Path’, ‘HTML options’– Add ‘_path’ to controller to get URL path (i.e. line_item_path)– Pass in hash values to URL path as parameters– id extracted from ActiveRecord objects passed in

• app/views/store/index.html.erb<%= button_to ‘Add to Cart’, line_items_path(:product_id => product) %>

Modify line_item create

• By default, create parameter is a serialized line_item object - params[:line_item]

• Create a line_item based on the product id and add it to the cart

Modify line_item create (cont.)

• app/controllers/line_items_controller.rb

Update the functional test

• test/functional/line_items_controller_test.rb

– assigns() accesses instance variables in the controller being tested

Try it out

• http://localhost:3000/

– Cart scaffolding didn’t show any attributes of what was just added

Modify the view

• app/views/cart/show.html.erb

<h2>Your Pragmatic Cart</h2><ul> <% for item in @cart.line_items %> <li><%= item.product.title %></li> <% end %></ul>

Try it out (again)

• http://localhost:3000/

– Cart now shows what is contained– Need to show each item only once (next chapter)

Homework

• Change the view so that clicking on a book’s image will also add the product to the cart

• Add a new session variable to record how many times the user accessed the store controller’s index action

• Add the counter to the template and display it on top of the catalog page

• Reset the counter to zero when adding to the cart

• Change template to display counter when > 5