Context aware authorization using CanCan

Question

I want to use CanCan to handle my permissions. My site has many different permissions levels, and most of them are context aware. For instance, Here are the relations in my 3 ma

Answer 1

Ok, I solved the problem. My use case is briefly mentioned in the beginning of the CanCan README and I missed it. You can define new Ability classes in app/models/ that take in a different parameter other than current_user. To do so, you put the following in your controller:

def current_ability 
  if params[:controller] == 'leagues'
    @current_ability = LeagueAbility.new(current_user_league_relation)
  elsif params[:controller] == 'league_relations'
    @current_ability = LeagueRelationAbility.new(current_user_league_relation)
  else
    @current_ability = Ability.new(current_user)
  end
end

Now you can create league_ability.rb in app/models/.

class LeagueAbility
  include CanCan::Ability

  def initialize(league_relation)
    league_relation ||= LeagueRelation.new

    if league_relation.owner?
      can :manage, League, :id => league_relation.league_id
    elsif league_relation.moderator?
      can :manage, League, :id => league_relation.league_id
      cannot [:delete, :destroy], League
    else
      can :read, League
      can :create, League
    end    
  end
end

One thing to note is that this relies on your application controller calling a method in a child class. Hope that helps!