Question

This is being more difficult than I thought: I am building a system in which users can have two roles: Sellers and Buyers. The architecture must meet this requirements:

• A user must be at least one of them, or both. The most common case will of course be Buyer.
• Each user type has its own profile, with different sets of fields
• When a user registers, one of either profiles must also be created and associated to it.
• Users will have different actions available depending on their type of profile.

I have considered different design patterns but I am not good at databases design, so I am nit sure which one to apply or how. I’ve already discarded STI, so I think the solution must be some kind of user has_many :profiles & buyer/seller belongs_to :user. But I am not sure if I should use polymorphism, through, or other kind of relationship.

Answer 1

I’ve built some applications that have similar requirements. I believe the best solution that would meet your requirements is has_many :through.

class Person < ActiveRecord
  has_many :assignments
  has_many :roles, :through => :assignments
end

class Assignment < ActiveRecord
  belongs_to :person
  belongs_to :role
end

class Role < ActiveRecord
  has_many :assignments
  has_many :people, :through => :assignments

  validates :name, :presence => true

  delegates :profile, :to => :assignment
end

Database:

 people
   |-- first_name, :string
   |-- last_name, :string

 assignments
   |-- person_id, :integer
   |-- role_id, :integer
   |-- profile, :text

 roles
   |-- name, :string