Error on rendering show action - ruby-on-rails

Question

I am trying to render show action by passing parameters, but the show page is not being rendered when there are no users signed in. This is my controller:
class QrCodesController < ApplicationController
def show
#user = User.find_by_qr(params[:id])
if #user.nil?
redirect_to root_path
end
end
end
and this is my view:
This is the qr-code page of <%= #user.fname %> <%= #user.lname%>
However, the show page is perfectly rendered when any user is signed in.
The rails server also shows perfectly rendered show action:
Started GET "/qr_codes/9M9JZLiemrNdS_g90mZ14w" for 127.0.0.1 at 2013-08-02 18:29:55 +0545
Processing by QrCodesController#show as HTML
Parameters: {"id"=>"9M9JZLiemrNdS_g90mZ14w"}
User Load (0.3ms) SELECT "users".* FROM "users" WHERE "users"."qr" = '9M9JZLiemrNdS_g90mZ14w' LIMIT 1
Rendered qr_codes/show.html.erb within layouts/application (0.7ms)
Rendered layouts/_shim.html.erb (0.0ms)
Web Load (0.3ms) SELECT "webs".* FROM "webs" WHERE "webs"."id" = 2 LIMIT 1
Rendered layouts/_header.html.erb (3.2ms)
Rendered layouts/_footer.html.erb (0.0ms)
Completed 200 OK in 54ms (Views: 52.4ms | ActiveRecord: 0.5ms)
I am using rails 3.2.13, ruby 1.9.3p429 along with devise 3.0.0. The User model was not generated by devise.
Please Help.
EDIT:
This is the link that triggers the show action:
http://localhost:3000/qr_codes/9M9JZLiemrNdS_g90mZ14w

Answer 1

Since #user is equal to # when you print it, it is clearly not equal to nil and the redirection is not happening. You need to either change the code in find_by_qr to return nil if not found, or determine what other way that that method is using to represent not found, and change your conditional to use that.

Answer 2

Try this instead:
#user = User.find_by_qr(params[:id])
if #user
respond_to do |format|
format.html
end
else
redirect_to root_path
end