Rails + simple role system through associative table

Question

So I have the Ninja model which has many Hovercrafts through ninja_hovercrafts (which stores the ninja_id and the hovercraft_id).

It is of my understanding that this kind of arrangement should be set in a way that the associative table stores only enough information to bind two different classes.

But I'd like to use the associative table to work as a very streamlined authorization hub on my application. So i'd also like this table to inform my system if this binding makes the ninja the pilot or co-pilot of a given hovercraft, through a "role" field in the table.

My questions are:

1. Is this ugly?

2. Is this normal?

3. Are there methods built into rails that would help me to automagically create Ninjas and Hovercrafts associations WITH the role? For exemple, could I have a nested form to create both ninjas and hcs in a way that the role field in ninjas_hovercrafts would be also filled?

4. If managing my application roles this way isn't a good idea, whats the non-resource heavy alternative (my app is being designed trying to avoid scalability problems such as excessive joins, includes, etc)

thank you

Answer 1

This might not answer you question completely, but if you are only going to have two roles for hovercrafts I would instead set up the associations like this

class Hovercraft < ActiveRecord::Base
  belongs_to :pilot, :class_name => 'Ninja', :foreign_key => 'pilot_id'
  belongs_to :copilot, :class_name => 'Ninja', :foreign_key => 'copilot_id'
end

class Ninja < ActiveRecord::Base
  has_many :pilotings, :class_name => 'Hovercraft', :foreign_key => 'pilot_id'
  has_many :copilotings, :class_name => 'Hovercraft', :foreign_key => 'copilot_id'
end

Now if you have more roles than that, or if you need more flexibility you can use a third model to link them together.

class Hovercraft < ActiveRecord::Base
  has_many :hovercraft_roles
  has_many :ninjas, :through => :hovercraft_roles
end

class HovercraftRole < ActiveRecord::Base
  belongs_to :hovercraft
  belongs_to :ninja
end

class Ninja < ActiveRecord::Base
  has_many :hovercraft_roles
  has_many :hovercrafts, :through => :hovercraft_roles
end

With a role attribute in HovercraftRole model to indicated if it is a 'pilot' or 'copilot'.