Permissions and roles stored in DB, rails 3.1 - ruby-on-rails-3

Question

In my app I want to implement roles and permissions in them in such way, that users admins can create new roles in their browsers. So I need permissions table and roles table, where every role is a combination of permissions. For now I used CanCan gem, but this behavior is not default for this gem and finally I got very complicated structure of roles and checking permissions. Can anybody tell me what gem provides this behavior or maybe I should make it without any gems?

Answer 1

See Abilities in Database and Ability for Other Users from the CanCan wiki:
class Ability
include CanCan::Ability
def initialize(user)
can do |action, subject_class, subject|
user.permissions.find_all_by_action(aliases_for_action(action)).any? do |permission|
permission.subject_class == subject_class.to_s &&
(subject.nil? || permission.subject_id.nil? || permission.subject_id == subject.id)
end
end
end
end
EDIT
Some load optimizations:
class Ability
include CanCan::Ability
def initialize(user, context = nil)
if context.nil?
can do |action, subject_class, subject|
user.permissions.find_all_by_action(aliases_for_action(action)).any? do |permission|
permission.subject_class == subject_class.to_s &&
(subject.nil? || permission.subject_id.nil? || permission.subject_id == subject.id)
end
elsif context == :post
can :manage, Post, :id => y
elsif context == :users
can :manage, User, :id => x
end
...
And in controllers:
class UsersController
protected
def current_ability
Ability.new(current_user, :users)
class PostsController
protected
def current_ability
Ability.new(current_user, :posts)