models/user.rb

user.rb

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  ROLES = %w[admin moderator author banned]

	def roles=(roles)
	  self.roles_mask = (roles & ROLES).map { |r| 2**ROLES.index(r) }.inject(0, :+)
	end
	
	def roles
	  ROLES.reject do |r|
	    ((roles_mask.to_i || 0) & 2**ROLES.index(r)).zero?
	  end
	end
end