ada-c14 / oo-composition-demo

Object Composition Live-Code

Learning Goals

• Have concrete examples and strategies of Ruby syntax that model one-to-one relationships
• Have concrete examples and strategies of Ruby syntax that model one-to-many relationships

What's in this Repo

• main.rb
  • This is a file that loads all of the other files. It contains recommended comments and puts statements about what to cover and how, though instructors should feel empowered to use or change whatever feels most appropriate
• order.rb
  • Defines the class Order with the attributes id and shipment
• shipment.rb
  • Defines the class Shipment with the attributes tracking_number
• merchant.rb
  • Defines the class Merchant with the attributes name and products
• product.rb
  • Defines the class Product with the attribute name

Instructors

You should be modifying your code on a new branch that is your class name, ie leaves, branches, sockets, ports, etc.

One to One Relationships

One to one relationships should be tracked using instance variables, named appropriately and singular, and assigning values to them.

To summarize:

• To read one-to-one relationships, we read instance variables using the dot syntax
• To set one-to-one relationships, we should be assigning values to instance variables

Demo

Run through the first comment section in main.rb.

Questions for during or after the Demo

Note the attr_accessor in the Order class. What attribute is attached to attr_accessor? Why couldn't it be attr_reader?

Optional: What alternative syntax could we use?

One to Many Relationships

One to many relationships should be tracked using instance variables, named appropriately and plural, and creating an empty array and modifying the array.

To summarize:

• To read one-to-many relationships, we read instance variables using the dot syntax and get back an array
• To set one-to-one relationships, we should be assigning values to instance variables, or pushing/modifying existing instance variables

Demo

Questions for during or after the Demo

Note the attr_reader in the Merchant class. What attributes are attached to attr_reader? Why do we not need attr_accessor?