Agile Web Development with Rails 6

Organizing Structures

Ruby has two basic concepts for organizing methods: classes and modules. We cover each in turn.

Classes

Here’s a Ruby class definition:

class Order < ApplicationRecord
   has_many :line_items
   def self.find_all_unpaid      
     self.where('paid = 0')
   end
   def total                     
     sum = 0
     line_items.each {|li| sum += li.total}
     sum
   end
end

Class definitions start with the class keyword, followed by the class name (which must start with an uppercase letter). This Order class is defined to be a subclass of the ApplicationRecord class.

Rails makes heavy use of class-level declarations. Here, has_many is a method that’s defined by Active Record. It’s called as the Order class is being defined. ...