Agile Web Development with Rails 7.2

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 < ActiveRecord::Base
   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 and are 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 ...