Cohabitant and Notification models

cohabitant.rb

class Cohabitant < ActiveRecord::Base
  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i

  validates_presence_of :department, :location, :contact_name, :contact_email
  validates :contact_email, :format => { :with => VALID_EMAIL_REGEX }
  
  has_and_belongs_to_many :notifications
end

notification.rb

class Notification < ActiveRecord::Base
  belongs_to :user
  has_and_belongs_to_many :cohabitants
end