Rails: How do I model preferences? Should I use ha

Question

I have two models: User and HairColor. A user has only one hair color, but can have many hair color preferences. What's the best way to model this?

Here's what I started to do:

#models/user.rb
class User < ActiveRecord::Base
  belongs_to :hair_color
  has_many :preferences, 
  has_many :hair_colors, :through => :preferences
end

#models/hair_color.rb
class HairColor < ActiveRecord::Base 
  has_many :users
end

#models/preference.rb
class Preference < ActiveRecord::Base 
  belongs_to :user
  belongs_to :hair_color
end

Is using has_many :through the right approach? Also what if I want to extend this to other attributes such as "eye color"? (A user has one eye color, but can prefer many eye colors"

Answer 1

There will be a limited amount of hair colors, so the preference table needs to have a hair_color_id and be set up like so:

#models/user.rb
class User < ActiveRecord::Base
  has_one :hair_color
  has_many :preferences
end

#models/hair_color.rb
class HairColor < ActiveRecord::Base 
  belongs_to :user
  belongs_to :preference
end

#models/preference.rb
class Preference < ActiveRecord::Base 
  belongs_to :user
  has_many :hair_color
end

I believe that's correct. Let me know if you run into any snags.

---

When you add eye color or any other characteristic, you'll probably have to do something different with preference. I'd have 4 columns at that point: id, user_id, foreign_id, foreign_type

foreign_id would be the id from the eye_color/hair_color table, and foreign_type would be "eye" or "hair" or something. Then in your model, you'd have something like this:

#models/hair_color.rb
class HairColor < ActiveRecord::Base 
  belongs_to :user
  has_many :preferences, :foreign_key => :foreign_id, :conditions => { "preferences.foreign_type" => "hair" }
end

That gets a little crazy, but it's the most DRY way of doing it. You'd put the same thing in your eye_color.rb and just replace "hair" with "eye" for the foreign_type.