How to setup a polymorphic association of People and Users?

Question

If there a People model, how can I setup a polymorphic association of Users and Customer?

For example, a Person could act as an User or as a Customer. People could be a User( extra columns: username, password), or it could be a Customer(no extra columns).

I'm trying to set this up so

1. I won't have a separate Users table and Customers table
2. I don't want to have a People table with a lot of empty username and password columns

Answer 1

I agree with moo-juice, the correct approach would be people + roles. here's a concrete example:

class Person < ActiveRecord::Base
  has_many :roles, :through => :roles_people
  #columns would be username, password, etc
end

class Role < ActiveRecord::Base
  has_many :people, :through > :roles_people
  #a column of role_type would be required here and the values of such would be Customer, User, etc.  in this class you will put logic that is needed to execute the functions of the role
end

class RolesPerson < ActiveRecord::Base
   belongs_to :person
   belongs_to :role
   #this is a join model for a many-to-many relationship. you can store info in here about when a person acquired a certain role, etc.
end