Creating a Scoped Invitation System for Rails (Example)

Context Assuming we have an app with some models that look like this: class User < ActiveRecord::Association has_many :memberships has_many :user_groups, through: :memberships end class UserGroup < ActiveRecord::Association #(Could be a company, club, circle, etc.) has_many :memberships has_many :users, through: :memberships end class Membership < ActiveRecord::Association #(Pass through model) be