Question

I’m using Rails 3.0.9 with cancan 1.6.7 and device 1.4.8

I’ve a doubt that, Does the can / can? / cannot / cannot? method invoke the current_ability method because

I just wrote the current_ability method in application controller which overwrites the cancan’s current_ability method

In apllication_controller.rb

    def current_ability
      if current_user.kind_of(User)
        @current_ability ||= UserAbility.new(current_user)
      else
        @current_ability ||= AdminAbility.new(current_admin)
      end
    end

Found that, this method is invoked 44 times per page request

the index page loaded after login contains 35 menu items (loaded using can? method) and content with 3 actions (loaded using can? method)
why current_ability method is invoked 44 times ?

Answer 1

Yes. Every can? cannot? and authorize! calls the current_ability method (See: CanCan’s controller_additions.rb)

Also, I wouldn’t worry about the 44 calls to current_ability. You’re only creating one Ability object per request because you are using an instance variable at the controller, with the ||= operator (i.e. memoization). It’s not a significant performance hit.

For example, let’s do a quick benchmark to fetch the same cached object 100,000 times…

require "benchmark"

def cached_object
  @foo ||= String.new('foobar')
end

cached_object.object_id.to_s(16)   # => 3ffc5cc53cb0
cached_object.object_id.to_s(16)   # => 3ffc5cc53cb0 (same object is returned)

Benchmark.bm(7) do |b|
  b.report("Cached Object") { 100000.times {cached_object}}
end

#               user     system   total     real
# Cached Object 0.010000 0.000000 0.010000 (0.017291)