Abilities in Database

What if a non-programmer needs to modify the user abilities, or you want to change them without having to re-deploy the application? In that case it may be best to store the permission logic in a separate model, let's call it Permission. It is easy to use the database records when defining abilities.

For example, let's assume that each user has_many :permissions, and each permission has "action", "subject_class" and "subject_id" columns. The last of which is optional.

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

An alternative approach is to define a separate "can" ability for each permission.

def initialize(user)
  user.permissions.each do |permission|
    if permission.subject_id.nil?
      can permission.action.to_sym, permission.subject_class.constantize
    else
      can permission.action.to_sym, permission.subject_class.constantize, :id => permission.subject_id
    end
  end
end

The actual details will depend largely on your application requirements, but hopefully you can see how it's possible to define permissions in the database and use them with CanCan.

You can mix-and-match this with defining permissions in the code as well. This way you can keep the more complex logic in the code so you don't need to shoe-horn every kind of permission rule into an overly-abstract database.

You can also create a Permission model containing all possible permissions in your app. Use that code to create a rake task that fills a Permission table: (The code below is not fully tested)

def setup_actions_controllers_db

  write_permission("all", "manage", "Everything", "All operations", true)

  controllers = Dir.new("#{RAILS_ROOT}/app/controllers").entries
  controllers.each do |controller|
    if controller =~ /_controller/
      foo_bar = controller.camelize.gsub(".rb","").constantize.new
    end
  end
  # You can change ApplicationController for a super-class used by your restricted controllers
  ApplicationController.subclasses.each do |controller|
    if controller.respond_to?(:permission)	
      clazz, description = controller.permission
      write_permission(clazz, "manage", description, "All operations")
      controller.action_methods.each do |action|
        if action.to_s.index("_callback").nil?
          action_desc, cancan_action = eval_cancan_action(action)
          write_permission(clazz, cancan_action, description, action_desc)
        end
      end
    end
  end
	
end


def eval_cancan_action(action)
  case action.to_s
  when "index", "show", "search"
    cancan_action = "read"
    action_desc = I18n.t :read
  when "create", "new"
    cancan_action = "create"
    action_desc = I18n.t :create
  when "edit", "update"
    cancan_action = "update"
    action_desc = I18n.t :edit
  when "delete", "destroy"
    cancan_action = "delete"
    action_desc = I18n.t :delete
  else
    cancan_action = action.to_s
    action_desc = "Other: " << cancan_action
  end
  return action_desc, cancan_action
end

def write_permission(class_name, cancan_action, name, description, force_id_1 = false)
  permission  = Permission.find(:first, :conditions => ["subject_class = ? and action = ?", class_name, cancan_action]) 
  if not permission
    permission = Permission.new
    permission.id = 1 unless not force_id_1
    permission.subject_class =  class_name
    permission.action = cancan_action
    permission.name = name
    permission.description = description
    permission.save
  else
    permission.name = name
    permission.description = description
    permission.save
  end
end